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Pr.ATK I. Grays Peak, Rocky Mountains of Colorado 



ELEMENTARY 



PHYSICAL GEOGRAPHY 



WILLIAM MORRIS DAVIS 

Sturgis-Hoopeb Professor of Geology in 
Harvard University 



Boston, U.S.A., and London 

GINN & COMPANY, PUBLISHERS 

Cl)e ^tlbensenm levees 

1902 



THE LIB 

eeNG 

Two Copifc" 

MAY. 6 ^902 

COPVRI»HT ENTRY 

0LA88 CL' XXc. No, 



X 



Entered at Stationers' Hall 



Copyright, 1902, by 
WILLIAM MOKRIS DAVIS 

all rights reserved 



PEEFACE 

The educational progress of recent years has resulted 
in two profitable advances for the venerable subject of 
Geography. A strong feeling has been developed in favor 
of treating the subject as a whole more rationally than 
heretofore, and a wholesome desire has arisen in favor of 
introducing some of its scientific aspects more generally 
into the school course. A natural accompaniment of this 
progress has been a demand for text-books that shall present 
Physical Geography in its modern scientific development 
as well as in an elementary form. The present book, 
reduced from the author's "Physical Geography," has been 
prepared to meet this demand. 

The reduction of the earlier book to the present volume 
has been made chiefly by omitting the more advanced 
problems and by simplifying and abbreviating the treat- 
ment of the remainder; but the chapter on The Atmos- 
phere is here given a greater length than before ; and a new 
chapter is added on The Distribution of Plants, Animals, 
and Man, considered from a physiographic standpoint. 
Several topics of a somewhat more advanced nature than 
the rest of the text, and yet of too great importance to be 
omitted altogether, are placed in supplements to Chap- 
ters I, II, and III. 



iv rilEFACE 

The plan of this volume is, like that of its predecessor, 
to give the problems of Physical Geography a rational 
treatment. The object of this method is not simply to 
explain physiographic facts, but through explanation to 
increase the appreciation of the facts themselves. It is, 
however, not enough that physiograpliic facts should be 
associated with their causes ; they must also be seen in 
relation to their consequences if their full importance is 
to be realized. This relation must not be presented merely 
as an afterthought, in a detached chapter at the end of a 
book ; it must accompany the presentation of the facts 
themselves. As Guyot long ago said so well: "To 
describe, without rising to the causes, or descending^ to 
the consequences, is no more science than merely and 
simply to relate a fact of which one has been a witness." 
The ideas of cause and of consequence, one preceding, 
the other following, the physiographic fact, have therefore 
been held constantly in mind by the author ; they should 
be no less constantly remembered by the teacher and 
impressed upon the pupil. 

Yet, while the causal notion is introduced as far as 
possible, it must be recognized that certain facts of great 
importance cannot be really accounted for in an elementary 
book. Such facts must therefore be described rather than 
explained. For example, the rotation of the earth and the 
separation of continental masses from ocean basins are 
subjects of great importance ; they must be described, and 
their consequences deserve careful attention, but their 
causes involve speculative investigation of a grade that 
far transcends the reach of an elementary text. Again, 



PREFACE V 

the simpler phenomena of the tides must be presented ; 
their period may be correlated with the movement of the 
moon, and the moon may be thus indicated as their chief 
cause ; but the relation between lunar cause and tidal 
effect cannot be demonstrated to young pupils. A mere 
outline of theory, with the briefest consideration of the 
joint action of sun and moon, is introduced in the sup- 
plement to Chapter III. 

The general circulation of the atmosphere is also far 
beyond elementary explanation. The circulation may be 
not unreasonably asserted to depend on the differences 
between equatorial and polar temperatures ; but the more 
intelligent the pupil, the less can he be satisfied with 
a simple conventional origin of the prevailing westerly 
winds. Explanation of this complicated problem is there- 
fore touched upon lightly ; while emphasis is given to the 
elements of which the circulation consists, to the correla- 
tion of these elements, and to the deduction of climatic 
conditions from them. The deflective effect of the earth's 
rotation is almost universally misunderstood, because it 
cannot be fully explained in an elementary manner. Its 
quality is briefly asserted in the text, and on account of 
its importance a correct explanation in the simplest pos- 
sible form is inserted in the supplement to Chapter II ; 
but neither this supplement nor that on the tides should 
be studied by the youngest pupils. 

On the other hand, the forms of the lands have not as a 
rule been sufficiently explained in text-books on Physical 
Geography. Fifty years ago there was justification for 
the empirical treatment and even for the neglect of land 



vi PREFACE 

forms, in the ignorance of geographers concerning their 
origin ; but the investigations of the hi,st thirty years have 
thrown a flood of light on this important division of the 
subject, and to-day it may be treated as rationally as any 
other. Many problems, formerly obscure, are now seen to 
be essentially simple and to lie entirely within the reach 
of elementary treatment. It has thus become possible to 
extend the explanatory method, long familiar in the study 
of the atmosphere and the ocean, to the lands as well ; 
and to present plains and plateaus, mountains and volca- 
noes, rivers, valleys, and shore lines under a rational 
system. It is believed that this division of the subject 
is here treated in a manner more systematic and compre- 
hensive and at the same time more simple and reasonable 
than is the case in any other elementary book. It should 
however be carefully borne in mind that the explanation 
of the processes which are involved in the dissection of 
a plateau, for example, is not introduced merely that the 
past history of the plateau shall become known, but 
chiefly that the existing features and especially the 
systematic correlation of these features shall be better 
perceived and remembered. 

While the list of topics treated will, it is believed, be 
found exceptionally full for an elementary book, it has 
nevertheless been necessary to go somewhat against time- 
honored traditions in omitting certain subjects. Elemen- 
tary text-books should not present an encyclopedic richness 
of contents, as if to show the learning of their authors ; 
they should provide a well-selected body of useful infor- 
mation having disciplinary value, pertinent to their subject 



PREFACK vii 

and appropriate to young pupils. It has therefore been 
decided to follow carefully the outline of Physical Geog- 
raphy lately prepared for and published by the National 
Educational Association, and to exclude certain traditional 
but irrelevant topics belonging properly to Astronomy, 
Geology, and Biology. It has also been deemed expedient 
to omit certain other relatively advanced topics ; such, for 
example, as the distribution of atmospheric pressure, shown 
by charts of isobaric lines, which have been, it may be said, 
fashionable since the publication of Buchan's excellent 
charts of these elements. Important as are the facts thus 
shown for the more advanced study of meteorology, they 
have no immediate climatic importance, and their proper 
use involves so many advanced considerations that they are 
best excluded from elementary study. Agam, there is a 
chart of cotidal lines, purporting to show the advance of 
the tidal wave through the oceans, which has been repeat- 
edly copied since it was first published by Whewell in 1833 ; 
but this pleasing generalization is omitted here because it 
was discredited by its very author in 1835, and because 
it has never since then received the approval of experts in 
tidal investigation. The best chart of cotidal lines, that 
of Berghaus' Physical Atlas (reproduced in the United 
States Coast Survey Report for 1900, Appendix No. 7, 
Figure 25), leaves the open oceans blank. 

The method of presentation adopted is sometimes induc- 
tive, sometimes deductive, according to the subject in hand. 
The inductive method is more largely used, because young 
pupils are as a rule better able to leam from direct descrip- 
tion than from inferences based on general principles. The 



viii PREFACE 

exercises suggested for the study of weather maps, in the 
supplement to Chapter II, are purely mductive ; and the sev- 
eral chapters on the development of land forms are largely 
inductive. But it must not be forgotten that the simpler 
processes of deduction are perfectly familiar to young 
pupils, and may be safely employed in teaching where 
they are appropriate to the topic in hand. It is indeed 
advisable that the pupil should gain some experience in 
deduction as well as in induction, and Physical Geography 
should be recognized as presenting ample opportunity 
for the exercise and development of both these mental 
processes. The relation of rainfall to the several mem- 
bers of the atmospheric circulation may be instanced as 
appropriately deductive, because of the systematic rela- 
tions of these topics. 

The illustrations in the chapters on land forms are of 
two kinds. The block diagrams represent ideal types. 
The views of actual landscapes in woodcuts and plates 
serve as examples of the ideal types. The block diagrams 
are in several respects more comprehensive than any 
actual view can be. They show so large an area, from so 
elevated a point of view, that the relation of the parts to 
the whole is easily perceived; they omit numerous and 
frequently irrelevant details by which the pupil's attention 
might be distracted ; they present in the most elementary 
manner possible the correlation of underground structure 
and surface form ; and in this respect they are far supe- 
rior to mere geological sections, in which the land surface 
is represented only by a profile line which few young 
pupils can translate into a topographic form. Exercises in 



PREFACE ix 

drawing simple outline maps from the block diagrams are 
frequently suggested, in order to insure the recognition 
of the essential features of the type. It will also be found 
useful to ask the pupil to indicate the relation of a view 
to its type diagram, as is done in the text for Figures 71 
and 73, and for Figures 141 and 142. 

The questions inserted in the text are intended to aid 
the pupil in learning his lessons ; the questions at the end 
of the chapters are intended for use by the teacher in tests 
and reviews after the lessons have been learned. If it is 
desired to extend the time devoted to Physical Geography 
by classes whose average age is somewhat above that for 
which tliis book may be used, all of the text, as well as the 
supplements to Chapters I, II, and III, may be studied in 
full. If it is desired to shorten the course, the supple- 
ments may be passed over, the number of map drawings 
may be decreased, and certain sections that are concerned 
with relatively advanced topics (for example, Sections 99, 
103, 107, 124) may be omitted. 

The teacher will find it practically convenient to indi- 
cate by a brief reference in the page margin the books and 
map3 mentioned in the Appendix. The examples there 
referred to should be supplemented as far as possible by 
local examples observable at or near the school. Illustra- 
tions of many topics treated in Chapter II will be found 
in the ordinary observation of passing weather phenomena. 
Many of the activities of the lands may be illustrated by 
local excursions, for which the autumn is a convenient 
season; while examples of the land forms seen in the 
school neighborhood should be studied m the spring. 



X PREFACE 

Inasmuch as land forms vary greatly from place to place, 
no general guide can be of service in this division of the 
subject; but teachers are advised to make themselves 
familiar with their school district by frequent excursions, 
and to use as far as possible all the appropriate illustra- 
tions that they discover. 

The author desires to express his thanks to a number of 
his correspondents who have supplied photographs from 
which several of the plates have been copied, and also to 
a number of teachers and others who have accepted the 
fatiguing task of criticising his manuscripts and proof, 
particularly to Professor J. B. Woodworth of Harvard 
University, Mr. M. Grant Daniell of Boston, and Mrs. 
M. A. L. Lane of Hingham. The questions at the ends 
of chapters have been prepared by Mr. R. H. Cornish, 
of the Girls' High School, New York, whose practical 
acquaintance with school work insures their value. 



W. M. D. 



Harvard University, 
Marcli, 1902. 



CONTENTS 

CHAPTER PAGE 

>'' I. The Earth as a Globe 1 

^ II. The Atmosphere ....... 23 

^ III. The Ocean 90 

/ IV. The Lands 129 

). V. Plains and Plateaus 141 

J) VI. Mountains 177 

''/ VII. Volcanoes 215 

VIII. Rivers and Valleys 234 

^ IX. Deserts and Glaciers ...... 278 

X. Shore Lines 304 

XT. The Distribution of Plants, Animals, and Man 332 



LIST OF PLATES 



I. Grays Peak, Rocky Mountains of Coloi'ado (photograph 
by W. H. Jackson) Frontispiece 

FACING PAGE 

II. A Sailing Vessel at Sea (by Neurdin) 40 

III. A. Cumulus Clouds ; B. Cirrus Clouds (by Riggenbach) . 63 

IV. Waterspout over Vineyard Sound, Aug. 19, 1896 (by 

J. N. Chamberlain) 67 

V. The Bore, or Surf-Like Flood Tide, in an Estuary at the 

Head of the Bay of Fundy, Nova Scotia . ... 121 

VI. The Great Plains (by W. D. Johnson) 159 

VII. A Railroad rounding a Spur of Mt. Ouray, Colorado (by 

W. H. Jackson) 191 

VIII. Grandfather Mountain, North Carolina (by A. Keith) . 205 
IX. A Water Gap in the Allegheny Mountains (by Maryland 

Geological Survey) 211 

X. Diuant on the Meuse, Belgium (by Neurdin) 258 

XI. The Braided Channels of the River Var in the Western 

Alps 261 

XII. Bad Lands in the Great Plains, South Dakota (by N. H. 

Darton) 283 

XIII. A Sand Dune rippled by the Wind (by G. K. Gilbert) . 287 

XIV. The Muir Glacier, Alaska (by H. F. Reid) 292 

XV. A Troughlike Glaciated Valley in the Western Alps (by 

Neurdin) 299 

XVI. A Land-Tied Island, near Genoa, Italy (by A. Noack) . 315 

XVII. A Branch of Sogne Fiord, Norvray (by A. Lindahl) . . 321 

XVIII. Forest in the Equatorial Rain Belt, Ceylon 348 

XIX. Moab, an Irrigated Settlement in Eastern Utah (by L. M. 

Prindle) 361 

xii 



LIST OF FIGURES 

FIG. • PAGE 

1. Eclipse of the Moon 2 

2. Height of Land and Depth of Sea 3 

3. The Shadow of a Box, showing the Altitude of the Sun . . 8 

4. Meridians and Parallels 9 

5. Latitude and Longitude 9 

6. Mariner's Compass 18 

7. Globular Form of Earth shown by Visibility of Stars ... 20 

8. Mercurial Barometer 25 

9. Mirage of Part of a Schooner, formed on a Thin Layer of Air 30 

10. The Comey Self-Recording Thermometer 32 

11. Illustration of an Isothermal Line 33 

12. Chart of Mean Annual Temperatures 34 

13. Anemometer 38 

14. The Planetary Circulation of the Atmosphere 40 

15. Wet- Weather Streams of the Tarso Mountains, Sahara . . 42 

16. Cyclonic and Anticyclonic Areas 45 

17. Monthly Positions of the Earth with Respect to the Sun . . 47 

18. Chart of Mean Temperatures for January 50 

19. Chart of Mean Temperatures for July 50 

20. Chart of Annual Range of Temperature 51 

21. Diagrams of Terrestrial Winds for January and July ... 53 

22. Winds of January 54 

23. Winds of July 55 

24. January Monsoons in Indian Ocean 57 

25. July Monsoons in Indian Ocean 57 

26. A Distant Thunderstorm .... 65 

27. Regions of Tropical Cyclones 68 

28. Chart of Mean Annual Rainfall 71 

29. Annual Rainfall of the United States 73 

30. Storm Tracks of the North Temperate Zone (after Loomis) 79 

31. Rotation of a Disk on a Rotating Globe 85 

xiii 



xiv LIST OF FIGURES 

FIG. PAGE 

32. Diagram of the Sun's Midday Altitude 88 

33. Diagram of Sunrise and Sunset Hours 89 

34. Water and Land Hemispheres 97 

35. An Ocean Steamship 98 

36. Sounding Instrument and Water Bottle 99 

37. Dredge 99 

38. A Vessel beset by Pack Ice 103 

39. An Iceberg 104 

40. Globigerina (magnified 100 time;;) . 105 

41. Section of Continental Shelf 108 

42. Orbital Movement of Water in Waves 109 

43. Surf 112 

44. Chart of Ocean Surface Temperatures and Currents . . . . 115 

45. Displacement of a Vessel by Currents 116 

46. Drift of Floating Objects by Currents 117 

47. Low Tide in a Harbor 120 

48. The Tidal Wave, or Bore, in the Seine 121 

49. Jellyfish fioating in Sea Water 122 

50. Deep-Sea Fish, x i 123 

51. Deep-Sea Crustacean, x i 123 

52. Earth and Moon 125 

53. Spring Tides, New Moon 125 

54. Neap Tide^, First Quarter 125 

55. Spring Tides, Full Moon .- 125 

56. Neap Tides, Third Quarter 125 

57. Variation of Tides for Two Weeks 126 

58. Height of Land and Depth of Sea 132 

59. A Quarry sh'owing Weathered Kock 135 

60. Mountains bordering the Sea '^~ T.42 

61. Sample Map of a Mountainous Coast 142 

62. Narrow Coastal Plain 144 

63. Sample Map of a Narrow Coastal Plain 145 

64. A Narrow Coastal Plain in Scotland 146 

65. Broad Coastal Plain 147 

66. Coastal Plain of the Carolinas 148 

67. A Truck Farm on the North Carolina Coastal Plain .... 149 

08. A Belted Coastal Plain 150 

69. Sample Map of Part of a Belted Coastal Plain 151 



LIST OF FIGURES XV 

FIG. I'AGE 

70. The Belted Coastal Plain of Southern New Jersey .... 153 

71. An Embayed Coastal Plain 154 

72. Sample Map of an Embayed Coastal Plain 155 

73. A Branch of Chesapeake Bay, Maryland 157 

74. Ancient Coastal Plain of Wisconsin 161 

75. A Plateau in Arizona 163 

76. Diagram of a Narrow Canyon 164 

77. Diagram of a Widened Canyon 165 

78. The Allegheny Plateau ' 168 

79. Canyon of the Kanawha River in Allegheny Plateau, W. Va. 169 

80. The Enchanted Mesa, New Mexico 172 

81. Broken Plateaus 173 

82. Hurricane Ledge, a Dissected Fault Cliff 174 

83. A Mountain Peak 178 

84. Block Mountains 179 

85. Mountains of Southern Oregon 180 

86. A Dissected Mountain Range, Utah 182 

87. Diagram of the Jura, a Folded Mountain Range 184 

88. Peaks of the Central Alps 186 

89. An Alpine Peak of Slanting Layers 187 

90. Path of an Ice Fall in the Alps 192 

91. The Landslide of Airolo, Switzerland 194 

92. A Landslide in the Himalayas 195 

93. The Himalaya Mountains 196 

94. Alluvial Fans 198 

95. A Filled Valley with a Flat Floor 199 

96. A Terraced Valley 200 

97. Railroad shaken by an Earthquake, Northeastern India . . 202 

98. Land Surface displaced by an Earthquake, Japan .... 203 

99. The Piedmont Belt, Virginia 206 

100. Map of the Piedmont Belt, Virginia 207 

101. The Upland of New England 208 

102. Valley of the Deerfield in the New England Upland ... 209 

103. Diagram of the Allegheny Mountains, Pennsylvania .... 210 

104. Model of Embayed Mountain.s 211 

105. Vesuvius in Eruption 217 

106. Monte Nuovo 218 

107. Cinder Cone and Lava Flow, California 220 



xvi LIST OF FIGURES 

FIG. PAGE 

108. Deception Island, a Volcanic Caldera (plan and section) . . 221 

109. The Cone of Vesuvius in tlie Caldera of Monte Somma . . 221 

110. Contour Map of Crater Lake in Mt. Mazama, Oregon . 222 

111. Excavations in Herculaneum 224 

112. Distribution of Volcanoes and Coral Islands 226 

113. Lava Flows on the Plateaus of Arizona 228 

114. The Lava Plateau of Idaho, Oregon, and Washington . . . 229 

115. Contour Map of Mt. Shasta, California . 230 

116. Mt. Shasta 231 

117. Map of the Lake Nicaragua District 232 

118. Diagram of Cavern and Sink Hole 235 

119. Section showing Ground Water in Rock Crevices beneath a 

Valley 237 

120. Diagram of a Coastal Plain with Artesian Wells .... 238 

121. A Geyser 240 

122. A Dividing Ridge in the Mountains of Northwest England . 242 

123. Niagara Falls 248 

124. Diagram of Niagara River between Lakes Erie and Ontario . 251 

125. Falls of the Yellowstone River 252 

126. Diagram of Torrent, with Falls and Reaches 253 

127. Valley of Yakima River, Washington 257 

128. The Mohawk Valley 258 

129. Outline Map of a Young Valley 259 

130. Diagrams of a Widening Valley 260 

131. A Meandering River, Vale of Kashmir, India 262 

132. A Meandering River on the Plain of Hungary 263 

133. Meandering Channel and Oxbow Lakes in the Flood Plain 

of the Mississippi ,. 264 

134. The Valley of California 266 

135. Torrent Fan Delta, Lake Geneva, Switzerland 267 

136. The Delta of the Mississippi 268 

137. Diagram of a Narrowed Spur in a Meandering Valley ... 272 

138. Diagram of a Cut-Off Spur in a Meandering Valley ... 272 

139. Intrenched Meanders of the Neckar 273 

140. Transverse and Longitudinal Streams . . , 274 

141. Transverse and Longitudinal Valleys 274 

142. Water Gap of the Susquehanna above Harrisburg, Pennsyl- 

vania 274 



LIST OF FIGURES xvii 

FIG. PAGE 

143. The Ozark Plateau, Missouri 279 

144. Glaciated Areas, Interior Basins and Ocean Deptlis . . 279 

145. Floo'd in Cherry Creek, Denver, Colorado 282 

146. Sand Dunes in the Sahara 287 

147. Lakes Bonneville and Lahontan 289 

148. Rosegg Glacier in the Alps 293 

149. Viesch Glacier in the Alps 294 

150. Glacial Moraines, Sierra Nevada, California 295 

151. Glaciated Area of the Northern United States 296 

152. Ice-Worn Rocks, Coast of Maine 297 

153. Glacial Moraines, North Dakota 298 

154. A Glacial Bowlder 298 

155t A Drumlin, Massachusetts 299 

156. A Side Valley hanging over the "Valley of the Ticino, South- 

ern Alps 300 

157. Lake in the Adirondacks, New York 301 

158. Sea Cliffs, Grand Manan, New Brunswick 305 

159. Diagram of a Lowland Coa.st with Bluff and Sand Reef . . 309 

160. The Sea Cliffs of Normandy (looking southwest) .... 311 

161. Diagram of an Irregular Shore Line 312 

162. Diagram of an Irregular Shore Line with Cliffed Headlands 

and Beached Bays 312 

163. Diagram of a Curved Shore Line 313 

164. A Cliffed Headland and a Land-Tied Island 314 

165. Gibraltar 315 

166. Diagram of a Group of Sea-Cut Islands 315 

167. A Cliffed Coast in Alaska . 316 

168. The " Old Man of Hoy " 317 

169. The Coast Platform of Norway 319 

170. A Delta in a Norwegian Fiord 321 

171. Deltas of the Texas Coast 322 

172. A Mangrove Tree 324 

173. ■ A Fringing Reef 325 

174. A Barrier Reef 325 

175. Part of the Great Barrier Reef of Australia (as seen at low 

tide, looking toward the mainland) 326 

176. Diagram of Part of a Barrier Reef 327 

177. Diagram of Part of an Elevated Reef with a New Fringing Reef 327 



xviii LIST OF FIGURES 

FIG. PAGE 

178. Diagram of an Atoll 328 

179. An Atoll, or Coral Island 329 

180. Beavers * . . 341 

181. Caribou 342 

182. Jaguar 343 

183. Kangaroo 344 

184. Cassowary 347 

185. Dwarfs in the Equatorial Forest . 351 

186. Eskimo hunting Walrus 352 

187. Gtunted Trees at the Tree Line on the Slope of Pikes Peak . 356 

188. Ibex 356 

189. The Yucca, a Desert Tree 360 

190. El Kantara Oasis, Algerian Sahara 362 



ELEMENTARY 
PHYSICAL GEOGRAPHY 

CHAPTER I 
THE EARTH AS A GLOBE 

1. Introduction. — Physical geography treats of the 
various features of the earth that influence the manner in 
wliich man lives upon it. Hence it must consider the 
form of the earth as a whole, the climates of its different 
parts, its oceans with their waves and tides, and the forms 
of its lands. 

It is the plan of this book to describe the more important 
kinds of physical features on the earth, to refer them to 
their causes in natural processes, and to trace them to their 
consequences as seen in the condition of mankind. 

2. The Shape of the Earth. — The people of savage races, 
when they think at all about the shape of the earth, gen- 
erally imagine it to be a great plain, varied by hills and 
mountains and surrounded by the sea ; for that is the 
appearance of the lands when seen from some high point, 
with mountains rising to greater heights, lowlands extend- 
ing to the seashore, and the ocean stretching beyond. 

The people of an ignorant race usually regard the place ' 
where they live as the center of the great earth plain. Of 



ELEMEXTAUY PHYSICAL GEOGRAPHY 



the ocean they know little ; its further parts are invisible 
and mysterious and are often thought of as much more 
dangerous than those which border the solid lands. 

Among the earliest observations that led to a knowledge 

of the true form of the earth were those made by the Greeks, 

The great philosopher Aristotle, who flourished about 

the middle of the fourth century B.C., made an ingenious 

use of the eclipses of the 
moon to determine the form 
of the earth. He knew that 
the eai'th cast a great shadow 
stretching away into space on 
the side opposite the sun; and 
that whenever the moon, in 
its movement around the 
earth, entered this shadow 
it was hidden or eclipsed, 
because it then no longer 
received the sunlight that 
Fig. 1. Eclipse of the Moon, show- Ordinarily makes it visible, 
ing the Curved Edge of the Earth's jje noted that the edge of 

Shadow , , , -, ■, 1 

the earth s shadow on the 
moon is a curved line, and thus he knew that the earth 
must have a curved surface, such as a globe has. 

The moon, revolving about the earth once in twenty- 
eight days, is not eclipsed every time it is opposite the 
sun, for it usually passes a little to one side of the earth's 
tapering shadow. 

The familiar ai'gument for the globular form of the 
earth, based on the disappearance of the lower part of 




THE EARTH AS A GLOBE 3 

distant vessels at sea, was not mentioned by ancient 
writers until about the beginning of the Christian era. 

3. Size of the Earth. — The earliest recorded measure- 
ment of the size of the earth was made by a Greek philos- 
opher in the third century B.C., who found its diameter to 
be about 8000 miles. The knowledge thus gained by the 
wise men of the ancient Mediterranean countries concern- 
ing the size and shape of the earth was unknown to the 
rest of the world and was afterwards forgotten ; but it was 
regained about the time of Columbus. 

The proof of globular form by sailing around the earth, 
or circumnavigation, was first accomplished in the sixteenth 



^$JJj;Ss<$^'yi^v:i^^;S;>^*^>^^<S:^^^N^^^^^^ -^ nnnxnwnnxn-- .^^^^^^x^.\^x^^\^vc^\•^\^-^^^;^^^ 



Fig. 2. Height of Land and Depth of Sea compared to Curvature of 
Earth's Surface 

century, when the Philippine islands were discovered. 
What can you learn about Magellan ? In later centuries 
nearly all parts of the earth have been explored, and its 
size and shape have been accurately measured. Its diam- 
eter is about 7912 miles. 

4. Unevenness of the Earth's Surface. — The broad 
depressions between the continents, in Avhich the oceans 
are gathered, are of small depth compared to the diameter 
of the earth. The continents have many mountains and 
valleys, but the general surface of the lands does not 
depart greatly from a globular form, such as is so Avell 
shown by the surface of the oceans. This is fortunate, 



4 ele:\ientaey physical geography 

for on very uneven lands the long ascents and descents 
between the higher and lower parts would make travel 
and transportation enormously difficult or utterly impos- 
sible. It is difficult enough to cross over the existing 
mountain ranges, whose highest peaks rise hardly more 
than y-qVo" ^^ ^^^® earth's radius and whose passes are much 
lower ; if their height were y^^- of the earth's radius, they 
would be absolutely impassable. 

Exercise. With chalk and string draw a circular curve of 4 feet 
radius on a blackboard. If the chalk line is ^^ hich wide, it 
will represent the average depth of the oceans (2 miles) ; if it is 
increased underneath here and there to ^ inch, it will indicate 
the greatest known depths of the oceans (about 5 miles). Small 
inequalities rising ^^^ to -^^ inch above the outside of the curved 
line will represent the altitude of the continents and their moun- 
tains above sea level. At a distance of 20 feet the departure of 
the curve from a true circle Mill be hardly noticed. So the earth 
would seem smooth and truly globular if we could see it from a 
great distance. 

5. Consequences of the Size and Shape of the Earth. — 

The earth is so large that savage tribes, even on the same 
continent, may remain in ignorance of each other for cen- 
turies. Each tribe then comes to have its own way of 
doing things, appropriate to its local surroundings. Thus 
differences of language and customs have originated. But 
since railroads and steamships have been invented the 
earth may be considered a relatively small body ; an active 
traveler may now visit nearly all its larger districts in his 
adult years. 

The civilized nations have become well acquainted witli 
each other, because the earth's suiface is so nearly \v\vl 



THE EARTH AS A GLOBE 6 

that movement over it is possible. They now maintain an 
international postal service, by which nearly 200,000 post 
offices are in regular communication with each otlier. The 
Roman alphabet is used by many nations, although their 
language may be different. The use of Arabic numerals 
is even more extended. The metric system of weights 
and measures is already widely introduced and will 
probably be adopted by all advanced nations during this 
century. 

The products of remote regions are exchanged, even 
from opposite sides of the earth. The wheat of one 
continent furnishes flour to another. Australian wool 
and meat are sold in London. The manufactures of 
Europe and the United States are distributed all over the 
world. On a more uneven earth it might be impossible 
to develop a world-wide commerce. 

6. The Earth's Attraction, or Gravity It is the attrac- 
tion of the earth, or terrestrial gravity, that causes bodies 
to have weight and to fall when not supported. Recog- 
nizing the earth to be a globe, " down " is toward its 
c^'.nter, or in the direction that bodies are pulled by its 
attraction, as indicated by a plumb line; "up" is away 
fiom the earth's center, or against the pull of gravity. A 
level surface, like that of a quiet body of water, a calm 
If^ke or ocean, represents a part of the convex or globular 
surface of the earth; it is everywhere at right angles to 
t)\e up-and-down, or vertical, lines. 

The stems and trunks of plants grow "up" against the 
force of gravity. Even on hillsides trees tend to grow 



6 ELEMEXTARY PHYSICAL GEOGRAPHY 

erect and not square out from the sloping surface. Many 
parts of the skeletons of men and animals, as well as many 
of their muscles, are especially adapted to bear the strain 
that is exerted upon them by the downward weight of the 
body. The habit of lying down to sleep has been formed ^ 
chiefly to rest the muscles that are in action while a per- 
son is standing. The walls of buildings are built vertical, 
because in that position they will stand most securely. 

7. The Earth's Rotation and its Consequences. — Few 
discoveries ever made by man have been more opposed to 
his early beliefs than that the earth turns or rotates on its 
axis once a day and . that it moves or revolves around the 
sun once a year; for nothing is more natural than to sup- 
pose that the firm earth stands still in the center of the 
universe and that all the bodies of the sky turn around it. 
But it has been proved that the apparent turning of the 
sun and stars around the earth from east to west is due to 
the actual rotation of the earth from west to east. One 
may gain a false impression of the same kind while look- 
ing from the window of a smoothly running train, when it 
seems as if the landscape moved backward instead of the 
train forward. The northern end of the imaginary line, 
or axis, on which the earth turns is directed (almost) 
toward the North Star in the sky. 

A little over two centuries ago it was discovered that 
the earth is not a perfect sphere, but is very slightly flat- 
tened at the poles. The equatorial diameter is 7926 miles ; 
the polar diameter, 7900 miles. This was explained by 
Newton as a result of the earth's rotation, and it may be 



THE EARTH AS A GLOBE 7 

taken as one of the best proofs that the earth and not 
the sky turns. 

8. Day and Night. — The sun illuminates one half of 
the earth, leaving the other half in shadow. As the earth 
turns around, passing from the light into the darkness, one 
perceives the succession of day and night every time a 
rotation is made. The time at which the sun comes in 
sight over the eastern horizon is sunrise; when it disap- 
pears below the western horizon, sunset. 

The succession of day and night, resulting from the 
rotation of the earth, has given man and many animals 
the habit of working in the light and resting in the dark- 
ness. The period of the earth's rotation furnishes a nat- 
ural unit of time, easily recognized and counted, and 
everywhere alike and constant. Clocks and watches are 
regulated to keep time with the earth's turning. The 
hour hand of timepieces in common use turns once for the 
average duration of daylight, and once for the average 
duration of darkness. 

The rotation of the earth, causing sunrise and sunset, 
suggests a natural system of directions by which the rela- 
tive positions of different places may be indicated. The 
cardinal points, east and west, north and south, are in a 
more or less definite way recognized by most peoples of 
the world. 

The sun rises through the eastern half of the sky dur- 
ing the morning and sinks through the western half in the 
afternoon. Midday is the moment when the sun passes 
the north and south line that divides the eastern from 



8 ELEMENTARY PHYSICAL GEOGRAPHY 

the western half of the sky. The sun then reaches its 
greatest height above the horizon; and, hence, at this 
moment a vertical rod casts the shortest shadow. 

Exercise. Set up a vertical post in level ground (or a square- 
cornered box on a level table). Mark the successive positions of the 
end of the rod shadovi^ (or of a corner of the box shadow) every ten 
or fifteen minutes for an hour or more before and after noon. Draw 




Fig. 3. The Shadow of a Box, showim; the Altitude of the Sun 



a line through the marks. Find the shortest line from the base of 
the post (or from the lower corner of the box) to the line through 
the marks. This shortest line is a true north line, or meridian (mid- 
day) line. On the following day note the moment when the shadow 
fails on the meridian line ; that moment is local solar noon, or mid- 
day. A watch then set to 12 o'clock will mark local solar time. 

9. Latitude and Longitude. — The north or meridian 
line would, if followed in the direction awa}^ from the 



THE EARTH AS A GLOBE 



sun, lead to the north pole ; in the opposite direction, to the 
south pole. All meridian lines therefore meet at the poles. 
When prolonged around the earth they are called meridian 
circles. Lines drawn at right angles to the meridians will 
run parallel to each other, east and west, around the earth 
and are therefore called parallels. The earth being globu- 
lar, a simple system of meridians and parallels may be 
imagined to form a network of circles over its surface. 




^'oulh Pule 

Fig. -l. Meridians and Parallels 




Fig. 5. Latitude and Longitude 



It is by reference to these lines that the relative positions 
of places on the earth's surface are determined. 

The parallel that lies halfway between the poles is 
called the equator. It divides the earth into the northern 
and southern hemispheres (half-spheres). The latitude of 
a place is its distance north or south of the equator. It is 
measured along the meridian of the place and is counted 
in degrees, ninety to a quarter circle. In Figure 5 the lati- 
tude of A is the number of degrees in the arc AC^ or the 
angle AOC, What is the latitude of 7>? 



10 ELEMENTARY PHYSICAL GEOGRAPHY 

Low latitudes are near the equator in either hemi- 
sphere; high latitudes, near the poles; middle latitudes, 
roughly midway between pole and equator in either hemi- 
sphere. (See page 89.) 

The longitude of a place is the number of degrees by 
which its meridian is east or west of a standard or prime 
meridian. The meridian of the national observatory of 
Great Britain at Greenwich, a suburb of London, is now 
very generally taken as the standard. The longitude of a 
place is measured from the prime meridian east or west 
along the equator to the meridian of the place and is 
counted in degrees, 180 to half a circle, or in hours, 
12 to a half circle. If NACS^ Figure 5, is taken as the 
standard or prime meridian, the longitude of B is measured 
by the arc CD of the equator, or by the angle COZ>, 
between the local and the prime meridians.. Is B in east 
or west longitude? What is the latitude oi Gl What 
is its longitude ? 

Practical Exercise. A useful illustration of the manner in which 
maps are rnade is given by providing a number of outline maps, 
showing parallels and meridians (latitude and longitude lines), on 
which the latitudes and longitudes of a number of points are to be 
platted. Tlie points should be selected on the boundary of some 
state or country ; their positions may be taken from ah atlas and 
written upon a blackboard. By drawing a line through the points 
thus platted each pupil will have constructed a rough map of the 
chosen boundary. Rivers and cities may be similarly located. 

Land surveys, by which the boundary lines of farms 
and house lots are marked out, are best made with refer- 
ence to the local meridian, or north line. Navigators have 



thp: earth A8 a globe 11 

daily occasion to determine their position with respect to 
the network of meridians and parallels, in order to follow 
the desired route, to avoid islands and headlands, and to 
reach their intended port. 

The boundaries of thinly settled parts of civilized 
nations and states are often defined by meridians and 
parallels, as between the western parts of the United 
States and Canada, as well as between many of the states 
themselves, and between the various parts of Canada and 
Australia. Thus great advantage is taken of the simple 
globular form and regular rotation of the earth, v 

10. Relation of the Earth to the Sun. — The sun, glow- 
ing with extreme heat, has the enormous diameter of 
866,500 miles. If the earth were placed at the sun's 
center, and the moon were moving around the earth at its 
actual distance of 240,000 miles, the sun would still reach 
almost 200,000 miles beyond the moon on all sides. 

So huge a body is a fitting center for the earth to move 
around. Even at the great distance of 93,000,000 miles, 
the brilliant sun gives abundant heat and light to the 
earth. This distance is so great that an express train 
traveling from the earth fifty miles an hour could not 
reach the sun in less than two centuries. 

The earth travels or revolves around the sun every year 
in a nearly circular path, called its orbit. In order to 
accomplish this long journey of over 600,000,000 miles, 
our globe rushes along at a speed of 18.5 miles a second, 
or over 1,500,000 miles a day. As the motion is accom- 
plished with perfect smoothness, and as we move with the 



12 ELEMENTARY PHYSICAL GEOGRAPHY 

earth, we are as unconscious of this rapid movement in 
the annual orbit as we are of the diurnal rotation on the 
axis. 

Exercise. Lay a large sheet of paper on a table; draw a line 
through the middle of the sheet. Let this line represent a distance of 
200,000,000 miles. On each side of the middle of the line set up a 
pin, so that the distance between the pins shall represent 3,000,000 
miles (^3_ of the length of the line). Lay off 189,000,000 miles on 
this scale on a thread and knot together the ends of this length, so 
as to make a loop. Lay the loop over the pins, stretch it tight witli 
a pencil point, and thus guided draw a curve around the pins. The 
line tlius drawn is nearly circular and represents the true form of 
the earth's orbit. Take out the pins. Around one pin hole draw a 
circle to scale, somewhat less than 1,000,000 miles in diameter ; 
this will represent the sun. On the same scale the earth would be a 
small dot. The points where the orbit is crossed by the middle 
line show the greatest and least distances of the earth from the sun. 
AATiat are these distances? The point nearest the sun (perihelion = 
"near-sun") is passed on January 1 ; the farthest (aphelion = « far- 
sun" ) on July 1. 

The stars are distant suns, shining by their owti light. 
Most of them are much more than a million times as far 
from the sun as the earth is. They are so exceedingly 
remote that a ray of light which travels from the sun to 
the earth in eight minutes would be about three and a 
half years on the journey to us from the nearest star. 
Many of the stars are believed to be larger than the sun. 

11. Relation of the Earth to other Planets There are 

a number of other bodies which, like the earth, move 
around the sun. Like the earth they do not shine by 
their own light, but only by sunlight that falls on them. 



TIIK EARTH AS A GLOBE 13 

At night these bodies look like stars, except that they 
twinkle less. Their light is brighter or fainter accord- 
ing to their size and their distance from the sun. The 
telescope shows them to be of globular form, like the 
earth. Their movement among the stars, easily noted 
from month to month, shows that they revolve around the 
sun in the same direction that the earth does. The spots 
that may sometimes be seen on the sun show that it also 
rotates on its axis in a little less than a month, in the same 
direction that the planets move around it. 

The planets that may be easily seen without a telescope 
are named Mercury, Venus, Mars, Jupiter, and Saturn. 
^Mercury, Venus, and Mars are smaller than the earth; 
Jupiter and Saturn are much larger. Mercury and Venus 
are nearer to the sun than the earth is ; Mars, Jupiter, and 
Saturn are more distant ; and two other large planets, 
Uranus and Neptune, are farther away than Saturn. The 
planets that are near the sun revolve around it in a shorter 
time (or "year") than those further away. The small 
planets, JNIercury and Venus, are believed to rotate very 
slowly on their axes, so that their "day" is long. The 
large planets, Jupiter and Saturn, rotate rapidly, so that 
th*eir day is about half as long as ours. 

The moon is a planetlike body which revolves around 
the earth while the earth revolves around the sun. The 
moon is therefore called a satellite (= a follower), because 
it accompanies the earth. Its diameter is about a quarter 
of that of the earth; its distance from the earth is about 
240,000 miles. Mercury and Venus have no satellites, Mars 
has two very small ones, Jupiter has five, Saturn has eight. 



14 



ELEMENTARY PHYSICAL aEOGRAPHY 



It is thus found that the earth is not a solitary body, 
unlike all others, but that it occupies an intermediate posi- 
tion in a large family of similar bodies. 

Diagrams may be constructed to represent the relative 
sizes of the planets and their relative distances from the 
sun by means of the following table. Diameters are given 
in thousands of miles ; distances in millions of miles. 





Distance 


Diameter 




Distance 


Diameter 


Sun ..... 





866. 


Jujiiter . . 


480 


85.3 


Mercury . . 


36 


3.0 , 


Saturn . . . 


881 


70.1 


Venus . . X 


67 


7.6 


Uranus . . 


1772 


30.9 


Earth .... 


93 


7.9 


Neptune . . 


2770 


34.0 


Mars .... 


141 " 


4.2 


1 







12. The Solar System. — The sun, the planets, and their 
satellites form a group of bodies called the solar system. 
The resemblances of form and motion among the planets 
and satellites are so numerous that it is believed that they 
have all had a common origin. It has been thought that 
these bodies, and the sun also, have been formed by the 
gathering together of materials that were once scattered 
through an enormous space, like a vast cloud or nebftla. 
This interesting and famous theory is called, the nebular 
hypothesis, but it is not successful in explaining all fea- 
tures of the solar system. "^ 

The stars resemble the sun in many ways. It is 
believed that each star may be accompanied by a larger or 
smaller family of planets ; and hence the number of earth- 
like bodies in the universe is probably very large. 



THE EARTH AS A GLOBE 15 

13. Structure of the Earth. — Rocks of one kind or 
another are often seen at the surface of the lands; or if 
the sui'face is covered by soil, rocks may be found beneath 
the soil in wells and railroad cuts. The deepest mines 
and borings, reaching about a mile beneath the surface, 
pass through similar rocky materials. Hence it is believed 
that the body of the earth is composed of rock. 

This great globe of rock is covered with a considerable 
quantity of water and air lying ujson its surface and 
forming its oceans and its atmosphere. The oceans are 
not continuous all over the earth, but are gathered on 
the lower parts of the surface, while the higher parts rise 
somewhat above the oceans and form the continents. The 
atmosphere entirely incloses the oceans and the continents, 
rising far above the highest mountains. 

Thus the earth as a whole consists of matter in three 
different states, — solid, liquid, and gaseous. The liquid 
portion, or water, is also known as a solid when it freezes 
and forms ice ; and as a gas when it evaporates and mixes 
with the air as invisible water vapor. The solid portion, 
or rock, is seen as a liquid when it comes forth from vol- 
canoes at high temperatures as molten lava. The gaseous 
portion, or air, is always gaseous under natural conditions, 
but it may be artificially reduced to a liquid or a solid b} 
subjecting it to heavy pressure at extremel}^ low tempera- 
tures. 

There is a certain amount of mixture of rock, water, 
and air, or of the solid, liquid, and gaseous parts of the 
earth. Some solid substances have been dissolved by the 
action of water and are now found in the oceans. A small 



16 ELE.MENTARY PHYSICAL GEOGRArHY 

amount of rock in very fine particles, or dust, is raised 
from barren surfaces by the wind and carried far and 
wide ; the finest particles remain long in the air, slowly 
settling but often lifted again by rising currents. Water 
and air penetrate all pores and crevices that they can find 
in the rocky sphere. Water vapor is always present in 
the atmosphere in small and variable proportion ; it becomes 
visible when chilled and condensed, forming small liquid 
or solid particles in cloud, rain, or snow. A small amount 
of air is dissolved in the oceans ; bnt for this, the fish and 
many other animals that live beneath the surface of the 
sea could not breathe. 

14. Underground Temperatures. — Temperatures meas- 
ured in deep wells and mines show that the earth becomes 
warmer beneath the surface. The average increase of 
temperature downwards is about 1° for sixty feet. At 
great depths, such as twenty or a hundred miles or more, 
very high temperatures would be expected ; they are proved 
to occur by the melted lavas that rise and escape in vol- 
canoes. It is therefore supposed that the great interior 
rocky mass of the earth is hot enough to be melted, 
although the enormous pressure of the outer parts may 
prevent the expansion that would be needed to make it 
liquid. It may thus be forced to remain solid in spite of 
its high temperature. The outer and cooler part of the 
^arth is often called its crust. 

Just as a hot ball of iron will cool when it is hung in 
the free air, so the earth must be slowly cooling as it 
moves through cold space. It is very probable that the 



THE EARTH AS A GLOBE 17 

unevenness of the geosphere, in ocean basins, continents, 
and mountains, is in some way the result of a sort of set- 
tUng and bending of the crust, slowly caused by the long 
cooling of the earth. 

15. Age of the Earth. — It is impossible to say what the 
age of the earth and the solar system is, but it certainly 
should be reckoned in millions and millions of years. 
There is every reason to believe that the sun and the 
planets existed for an indefinitely long period before the 
condition of the earth's surface was such as to allow 
the habitation of the planet by plants and animals. It is 
well proved by the prints or fossils of various plants and 
animals in ancient rock layers that these lower forms of 
life existed upon the earth for a vast length of time, 
millions and millions of years before man appeared. It 
seems entirely possible that other planets may have once 
been, may now be, or may yet come to be occupied by 
inhabitants of some kind. 

16. The Earth as a Magnet. — If a magnetized bar of steel 
is balanced on a pivot and placed in the neighborhood of a 
large magnet, the direction in which the small bar points 
will be determined by its large neighbor. This may be 
tested by changing the relative positions of the two. If the 
small magnet is left alone, it will in most parts of the earth 
turn until it points about north and south. This is because 
the earth acts as if it were a huge magnet and so determines 
the direction in which smaller magnets tend to stand. 

The behavior of suspended bar magnets makes them 
very valuable in determining directions, especially in 



18 



ELEMENTARY PHYSICAL GEOGRAPHY 



cloudy weather at sea. A magnet mounted in a con- 
venient case is called a compass, the bar being called a 
needle. In the mariner's compass a card bearing the 
letters indicating the points of the compass lies on the 
needle and turns with it. 

The needle seldom points along a true meridian toward 
the pole, but somewhat to one side or the other of a 
meridian, in a direction that if followed will lead toward 
the " north magnetic pole " (about twenty degrees away 

from the true north pole 
toward Hudson bay) or 
toward the "south mag- 
netic pole " (about the 
same distance from the 
true south pole toward 
New Zealand). The dif- 
ference between true 
north and magnetic 
north at any place may 
be determined by com- 
paring the direction of the midday (or shortest) shadow 
cast by a vertical pole with the direction of a compass 
needle. 




Fig. (i. Mariner's Compass 



17. The Aurora. — During clear nights, especially in 
winter time, the northern part of the sky is sometimes 
illuminated by an arch of whitish, greenish, or rosy light. 
Moving streamers of light, whitish or colored, are seen 
between the arch and the higher parts of the sky. This 
appearance is called the aurora borealis, or "northern 



THE EARTH AS A GLOBE 19 

lights." The aurora is more frequent and brilliant in 
high northern latitudes than in temperate latitudes. A 
similar appearance in far southern latitudes is known as 
the aurora australis. In both cases the middle of the 
auroral arch is seen in the direction of the magnetic pole. 
From the disturbance of delicate magnets during an 
auroral display it is believed that the lights are due to a 
faint electric discharge controlled by the magnetic forces 
of the earth. 

Supplement to Chapter I 

18. Proof of the Globular Form of the Earth by Observations of the 
Stars. — Looking upward from the earth, the sky seems like a hoUov/ 
shell of vast size, carrjdng the sun by day and the stars by night. 
The earth may be thought of as standing at the center of the great 
sky shell, so that an observer at any point sees only half the sky 
above him, the other half being hidden beneath' the earth. The 
lower border of the visil)le half of the sky is called the horizon, and 
the plane that extends outward from the observer to the sky border 
is called the plane of the horizon. 

By watching through the night tiie Greek philosophers saw the 
stars rising in the eastern side of the sky and descending in the 
western; and they concluded that the sky, carrying the stars with 
it, turned around the earthy once a day. It is now known that the 
earth turns, and not the sky. 

In order to understand this clearly the pupil should learn by 
observation something of the diurnal movement of the sun, moon, 
and stars across the sky and should recognize that their paths are 
parts of slanting circles. 

Perception of the essential facts is greatly aided by tlie use of a 
"pointer," three or four feet long, tied at one end to the top of a 
stake about which it may turn freely. Direct the pointer toward the 
sun at different hours of the day. Repeat this until the (apparent) 



20 



ELEMENTARY THYSICAL GEOGRAPHY 



movement of the sun becomes familiar. Then sweep the pointer 
more rapidly through its successive i^ositions. Infer the directions 
it would assume if the sun could be observed all night. Infer the 
attitude of a line, or axis, about which the pointer turns. This line 
must be parallel to the axis on which the earth turns. 

The (apparent) diurnal rotation of the stars is best shown by home 
observations. Direct a pointer toward a star at a convenient evening 
hour. Watch the star for five or ten minutes and note its change of 
position. The next evening begin the observation fifteen or twenty 
minutes earlier. How can the facts thus observed be best accounted 

for? The movement of 
-^^ ^^ * . -IT the stars as seen from dif- 

ferent places must next 
be considered. 

When one travels 
southward from B to C 
it is found that new 
groups of stars, Z, 
Figure 7, not visible 
before, come into sight 
over the southern horizon, while other groups, X, that had before 
been seen over the northern horizon are no longer visible. From 
this it is concluded that the plane of the horizon HJ at the new 
point of observation is not parallel to the plane FG at the first 
point, and that the surface of the earth must be convex instead of 
flat. Hence the earth as a whole must be a globe or sphere. 

Changes of this kind are easily recognized in traveling from the 
northern to the southern border of the United States, or farther 
south into Mexico or Cuba. They may be verified by correspond- 
ence between different schools, several hundred miles apart north 
and .south. What changes would be noted in traveling northward 
from Bto A? 




Fig. 7. 



Globular Form of Earth shown by 
Visibility of Stars 



THE EARTH AS A CxLOBE 21 

QUESTIONS 

Sec. 1. What are the chief subjects that are taught in Physical 
Geograpli y ? 

2. What is the view generally held by savage races as to the size 
and shape of the earth ? When were correct notions first gained as 
to the earth's shape ? How did Aristotle infer the earth's shajie ? 
What must be the relative iwsitions of sun, earth, and moon when i/ 
the moon is eclipsed? AVliy is the moon not eclipsed every month? 

3. AVhen was the earth's size first determined? When and by 
whom was tlie earth first circumnavigated? Name some of the 
places then discovered. 

4. Describe the general form of the earth. State the relation of 
its mountain heights and ocean depths to its diameter. Does the 
earth's form favor travel and transportation? How? 

5. How are savage tribes affected by the size of the earth? In 
what ways have civilized nations become associated with one 
another? 

6. What is meant by " iip " and " down " ? How is the siirface f 
of a quiet body of water related to the direction of gravity ? How 

is the position of tree trunks and house walls related to the direction 
of gravity ? AVhat consequences of the action of gravity are seen in 
men and animals ? 

7. What is the belief of j^rimitive man about the position of the 
earth? What are the facts? What is the effect of the earth's rota- / 
tion on its form ? 

8. What is the cause of day and night? What is the most ' 
natural unit of time ? What habits of man and animals result from 
the earth's rotation? How are the cardinal points related to the 
eai-th's rotation? What is the position of the sun at midday? How 
are midday and true north determined? Given a north and south 
line, how can vou determine east and west? 

...... y 

9. Define mei'idian line, meridian circle, poles, parallels, equator. 
What is latitude and how is it measured? What is meant by low, i/ 



22 ELEMENTARY PHYSICAL GEOGRAPHY 

middle, and high latitudes ? AVhat is longitude and how is it meas- 
ured? State some of tlie practical uses of meridians and parallels. 

10. Compare the sun's size with that of the moon's orbit. Calcu- 
late the time needed for an express train to reach the sun. What is 
the earth's orbit? What is the earth's orbital velocity? How is it 
found ? What are the stars ? What can be said of their distance 
from us ? 

11. How are the planets distinguished from the stars? Which 
planets can be seen without a telescope ? Name the planets in order 
of distance from the sun. Which are larger, which smaller, than the 
earth ? Compare the " day " of Jupiter and of Saturn with our day ; 
the " year " of Venus and of Mercury with our year. State the size 
and distance of the moon. 

12. What is the solar system? What features are possessed in ^ 
common by its members ? What do these common features suggest? 

13. Of what is the great body of the earth believed to consist? i/ 
Why ? What is meant by the earth's crust ? What are the three / 
states of matter? Give examples of them. What are the chief 
divisions of the earth? 

14. AVhat is known about underground temperatures? At what 
rate does temperature increase downward? What is the supposed 
condition of the earth's interior? What relation is suggested 
between the earth's surface form and its interior temperature? 

15. What may be said of the earth's age and of life on the 
earth ? 

16. How is a small balanced magnet affected by a large one? 
How will a balanced magnet stand when alone? What is a com 
pass ? What are the magnetic poles ? Where are they ? How far 
to one side of the meridian does the compass point at your school . 
Does it point east or west of the true meridian ? 

17. Describe the aurora borealis. How is it related to the mag- 
netic pole ? 



CHAPTER II 
THE ATMOSPHERE 

19. The Atmosphere is a light and transparent mixture 
of gases, known as air. It rests upon the lands and seas, 
forming the outermost part of the earth. It takes part in 
the earth's daily rotation and yearly revolution. 

Many processes that take place on the lands and seas 
depend on the atmosphere. The waves and currents of 
the ocean are caused by the winds ; the soil that covers 
so large a part of the lands results from the decay of the 
underlying rocks, largely through the action of moist air. 
Rainfall, so important in many ways, is supplied by mois- 
ture received from the oceans and carried about by the 
movements of the atmosphere. 

The atmosphere far overtops the highest mountains.- 
Meteors, or "falling stars," — small scraps of matter dash- 
ing toward the earth from outer space — are heated by 
rushing through the air at enormous speed, so that they 
become luminous. They are sometimes seen at heights 
of more than a hundred miles, showing that some air 
reaches that great altitude. 

Cloud, haze, and dust make the lower air more or less 
turbid and often shut out a great part of the sun's rays ; 
but when the air is clear it is so transparent that sunlight 
is strong even at the bottom of the atmosphere. 

23 



24 ELEMENTARY PHYSICAL GEOGRAPHY 

20. Composition of Air. — Air consists of a uniform 
mixture of gases in which a small and variable quantity 
of water vapor is usually present. The chief gases are 
nitrogen and oxygen, which constitute about four fifths 
and one fifth, respectively, of the atmosphere. 

Fire is the result of an active combination of some burn- 
able substance with the oxygen of the atmosphere. The 
heat thus developed may produce light, or it may con- 
vert water into steam, and the expansive force of the 
steam may be used to drive engines, and many kinds of 
machinery. 

All animals and plants breathe in air and use some of 
its oxygen to combine with part of their substance in a 
very slow combustion, which produces a slight amount of 
heat, but no fire. Thus all forms of life, animal and vege- 
table, depend u^jon the oxygen of the air, as well as upon 
their food, to keep them alive. 

Carbonic dioxide, constituting less than a thousandth 
part of the atmosphere, is nevertheless important for the 
growth of plants. The carbon taken from this gas by 
growing plants makes a large part of their structure. 

21. Pressure of the Atmosphere. — Although the air is 
invisible, it is attracted by the earth and exerts a pressure 
of about a ton to the square foot upon the surface on 
which it rests. The total pressure on a man's body 
amounts to several tons ; but this is not felt because the 
air within the body exerts a corresponding pressure out- 
ward. The air is so easily moved that little resistance is 
noticed when one walks through it ; but fast railroad 



THE ATMOSPHERE 



25 



^ 



trains are much impeded by the resistance of the air that 
they have to push rapidly aside. 

The pressure of the atmosphere is measured by the 
barometer. This instrument is of two kinds. 
The mercurial barometer, Figure 8, consists of 
a glass tube, somewhat more than thirty inches 
long and closed at one end. It is prepared by 
filling the tube with, mercury, closing the open 
end with the finger, and inverting the tube ; 
the open end is then placed in a vessel of mer- 
cury and the finger is withdrawn. The mei 
cury sinks a little below the closed upper end 
of the tube, leaving an empty space, or vacuum 
above it. The mercury column must presi 
down on part of the mercury in the vessel 
just as much as the air presses on any equal 
part of the mercury surface. Thus the height 
of the mercury column, measured by a scale 
may be taken as a measure of the pressure o:t 
the atmosphere. 

The aneroid barometer consists of a smal' 
box, from which the air has been exhausted 
A variation in the pressure of the atmospher< 
causes a slight change in the shape of th( 
box. The change is magnified by a series Oi. 
delicate levers, by which an index is moved 



on a dial. The reading indicated on the dial 



Fig. 8 

Mercurial 

Barometer 



then shows the pressure of the atmosphere. 

The ordinary changes of atmospheric pressure, such as 
may be seen to accompany weather changes by reading a 



26 ELEMENTARY PHYSICAL GEOGRAPHY 

barometer from hour to hour and from day to day, are 
seldom more than a thirtieth or a fifteenth of the total 
pressure. 

If a barometer is carried up a lofty mountain, leaving 
much of the atmosphere beneath it, the pressure of the 
overlying atmosphere is found to be much reduced. An 
ascent of a thousand feet causes a lowering of about an 
inch in the barometric column. Thus barometers may be 
used to measure mountain heights. 

Although very light, the air supports the flight of birds 
and insects. The wind drives sailing vessels and wind- 
mills. In dry regions, where the ground is not covered 
with vegetation, the shape of the surface is changed by the 
long-continued action of the wind in drifting sand and 
dust from place to place. 

22. Elasticity of the Air. — Air is extremely elastic, 
changing its volume with every change of pressure. Its 
lower part is compressed by the weight of the overlying 
parts, so that much more air is contained in a cubic foot 
at sea level than at a height of three miles. This is 
expressed by saying that the density of the lower air is 
greater than that of the upper air. A cubic foot of air at 
sea level weighs about 0.075 pound, while at three miles 
above sea level its weight is only about half as much, and 
at an altitude of a hundred miles the air must be almost 
imperceptible. 

Men and animals living on high plateaus have become 
accustomed to the rarity or thinness of the air around 
them. There are villages on the plateau of Tibet and in 



THE ATMOSPHERE 27 

the liiglier valleys of the Andes at heights of from 12,000 
to 14,000 feet, where the density of the air is hardly two 
thirds of that at sea level. Mountain climbino- at alti- 
tudes above 20,000 feet is almost impossible, from the 
difficulty of breathing the thin upper air. 

It is by slight wavelike movements in the air that 
sound is transmitted. So quickly is the wavelike dis- 
turbance passed on that sound travels a mile in five 
seconds. So easily is the air disturbed that a locust 
(cicada) may set hundreds of tons of air vibrating per- 
ceptibly to our nerves of hearing. When the volcano 
Krakatoa, between Java and Sumatra, exploded in August, 
1883, sounds were heard for 2000 miles, and atmospheric 
waves, detected by slight changes of pressure in barom- 
eters, passed three times around the earth. 

23. Colors of the Atmosphere. — The clear atmosphere is 
so transparent that the light of faint stars can pass through 
its whole thickness. In the daytime the sun lights up 
the sky so brightly that stars are not seen. The blue 
color of the clear sky is due to the scattering of sunlight 
on countless numbers of extremely minute particles, the 
scattered light being seen against the darkness of outer 
space. The red and yellow colors near the horizon at sun- 
rise and sunset are due to the sifting out of other colors as 
the sunlight passes obliquely through a great thickness of 
atmosphere. 

As the sun sinks slowly below the western horizon 
after a clear sunset, a pink or rosy arch of sunlit air — 
the twilight arch — may be seen slowly rising over the 



28 P^LEMENTARY PHYSICAL GEOGRAPHY 

eastern horizon; the dull blue sky below the arch is dark- 
ened by the shadow of the earth. A similar arch and 
shadow may be seen sinking in the west before a clear 
sunrise. Thus the shadow of night may be seen follow- 
ing the sunlit air of one day and disappearing before the 
sunlight of the next. 

24. Temperature of the Atmosphere. — -' The temperature 
of the land and sea surface and of the atmosphere is con- 
trolled by the rays of the sun. The temperature of the 
atmosphere is not much affected directly by the sun's rays, 
because the air is so transparent that the rays are very little 
taken in or absorbed by it; hence the upper air is every- 
where cold. The temperature of the lower air is largely 
controlled by the temperature of the land or sea surface on 
which the air rests. The sea surface absorbs the sun's rays 
somewhat more actively, and the land surface much more 
actively, than the air does ; thus they become warmer than 
the air. The air lying next to the heated surface is then 
warmed by heat that is carried or conducted from the land 
or sea to the air. 

At night, when sunshine is absent, land, sea, and air cool 
by radiating their own heat {giving out rays) toward outer 
space. Just as the air absorbs the rays of the sun very imper- 
fectly in the daytime, so it gives up very little of its own 
heat by radiating at night. The sea surface is somewhat 
more active than the air in cooling by radiation at night, 
and the land surface is much more so. Hence the lower air 
is cooled at night by conduction of its heat to the cooling 
surfaces on which it rests. In the upper air tlie diurnal 



THE ATMOSPHERE 29 

range or the change of temperature from day to night is 
very small ; it is somewhat greater in the lower air on the 
oceans ; it is much greater in the lower air on the lands. 

The sun's rays fall almost vertically on every part of the 
earth's surface near the equator for several midday hours, 
and there high temperatures must prevail. The rays fall 
obliquely on the polar regions, so that each ray is there 
spread over a larger surface than in the torrid zone, and 
its noon effect is no greater than that of an early morning 
or afternoon ray near the equator ; hence low temperatures 
must prevail around the poles. This may be illustrated 
by the difference in the heating effect of sunshine on the 
two slopes of a road that runs north and south over a hill. 
Between poles and equator intermediate temperatures are 
maintained. 

High, medium, and low temperatures are thus distrib- 
uted in belts — hot, medium, and cold — roughly parallel 
to the equator; the belts are known as the torrid, tem- 
perate, and frigid zones. Fortunately the cold or frigid 
areas occupy a relatively small part of the world. 

Yet even in the torrid zone lofty mountains rise into 
air that is so cold that snow lies on their upper parts all 
the year round. The lower limit of the permanent snow 
fields is called the snow line. It is about three miles 
above sea level in the mid-torrid zone ; about a mile above 
in latitude 55° or 60° N. or S.; it descends to sea level 
within the frigid zone, whei'e peimanent snow may be 
found even on the lowlands. 

Heated air expands. Hence, volume for volume, hot 
air is lighter than cold air ; the air of the torrid zone is 



30 



ELEMENTARY PHYSICAL GEOGRAPHY 



lighter than that of the frigid zones. This fact will be 
found of great importance as a cause of the winds. 

25. Mirage. — A curious consequence of the strong 
control of air temperature by that of the land or sea sur- 
face on which the air rests is sometimes seen in the reflec- 
tion of distant objects by the lower layer of air when its 
temperature is distinctly unlike that of the overlying air. 
A reflection of this kind is called a mirage (French, mean- 
ing "reflection"; pron. meerahzh). Its cause is as follows: 




Fig. y. jNIirage of Part of a Schooner, formed ou a Thin Layer of Air 

The surface of a level desert in a warm zone becomes 
very hot under unclouded summer sunshine, and the air 
close to the ground is heated by conduction, so that it 
becomes much hotter than that three or four feet higher. 
The upper surface of the hot air acts like a mirror and 
gives an inverted reflection of objects beyond it. The 
reflecting air surface thus imitates a water surface so well 
that travelers are often deceived by it and think that a 
lake exists where in reality there is nothing but dry 
sand. 



THE ATMOSPHERE 31 

When cold air blows over a warmer sea its lower layer 
may be heated by conduction from the water, so as to 
become distinctly warmer than the air at a greater height. 
When warm air blows over a colder sea the lower part 
may be cooled by conduction. In either case the lower 
layer may reflect the figure of distant vessels, the reflected 
image being seen upside down beneath the object itself, if 
the lower layer of air is thin and the observer is above it ; 
but above the object itself, if the lower layer is thicker 
and the observer is within it. s 

The equivalent of a mirage may often be seen by look- 
ing close along a brick wall that is exposed to strong sun- 
shine in calm warm weather. Objects that are nearly in 
line with the wall may be seen reflected on the film of hot 
air next to it. 

26. Thermometers. — The temperature of the air and 
of other bodies may be measured by the thermometer 
(temperature measure), consisting of a fine tube opening 
into a bulb at its lower end and containing mercury (or 
other liquid). The glass and the mercury take the tem- 
perature of the surrounding air. If warmed, both expand, 
but the liquid mercury expands more than the solid glass, 
and part of the mercury is therefore pushed from the bulb 
into the tube ; if cooled, both contract and some of the 
mercury is withdrawn from the tube into the bulb. Thus 
the height of the mercury in the tube measures relative 
heat and cold, or temperature. 

In the United States and Great Britain it is still 
customary to employ the Fahrenheit thermometer (F.), 



32 



ELEMENTARY PHYSICAL GEOGRAPHY 




Fig. 10 

The Comey Self-Recording 

Thermometer 



marking 32° at the freezing point and 212° at the boiling ; 
point of water. In continental Europe the Centigrade 
thermometer (C.) is used, reading 0° at the freezing and 
100° at the boiling point. 

Some thermometers are arranged so as to give a contin- 
uous temperature record in a curve drawn on a sheet of 
paper; such instruments are called self-recording ther- 
mometers, or thermographs, 
one pattern being shown in 
Figure 10. Others are con- 
trived so as to register the 
highest (maximum) and low- 
est (minimum) temperatures 
of the day; this is sometimes 
done by placing an index or 
short piece of fine wire inside 
the tube, so that it may be 
pushed up or down as the 
liquid expands or contracts. 
Such instruments are called 
maximum and minimum ther- 
mometers. 
When the thermometer is used to measure the tempera- 
ture of the air it should be suspended so as to be protected 
from direct sunshine and from rain and snow, but exposed 
to the wind. If placed outside of a window, the thermom- 
eter should be on the north side of the building, free from 
the wall and where warm air escaping from windows 
cannot affect it. It is better placed in a special shelter, 
away from buildings and trees. 



THE ATMOSPHERE 



33 



i^.S 



1 


1 

27 

( 


""■""i 


V 


23 i 


\ 

30 



27. Temperature Charts and Mean Temperatures. — The 

distribution of temperature is indicated on charts by lines 
drawn through places having the same temperature. 

Figure 11 gives the degrees of temperature prevailing 
over the middle and eastern United States on a certain 
morning. The dotted line is drawn so as to separate 
all places having 
higher temperatures 
(warmer) than 40° 
from those having 
lower temperatures 
(colder). Similar 
lines may be drawn 
for temperatures 
of 10°, 20°, 30°, 
50°, and 60°. Each 
of these lines is 
called an isother- 
mal (equal tem- 
perature) line, or 
isotherm. It is a 
line of uniform temperature, separating regions of higher 
and lower temperature. 

In the example here given all the states northwest 
of a line drawn from the southwest corner of Arkan- 
sas to the western end of Lake Erie have temperatures 
lower than 40°. All the states southeast of this line 
have temperatures higher than 40°. Many illustrations 
of this kind are afforded by the daily weather maps 
issued by the national Weather Bureau. What would be 




ysr--^S 



Fig. 11. Illustration of an Isothermal Line 



34 



ELEMENTARY PHYSICAL GEOGRAPHY 



the temperature of a place halfway between the isotherms 
of 50° and 60°? 

If records of temperature are kept at regular hours 
every day for a month, the hours being chosen so as to 
include the cooler as well as the warmer periods of the 
day, the sum of all the temperatures divided by the 
number of observations will give the average or mean 




Fig. 12. Chart of Mean Annual Temperatures 

temperature of the month. Similarly, if observations are 
kept up through a whole year, the mean temperature of 
the year may be determined. The mean temperatures 
of a place for a year usually differ by a small amount in 
successive years ; hence the standard mean annual tempera- 
ture of a place is determined by averaging the means of 
ten or twenty successive years. Observations of temper- 
ature have now been made during many years at a great 



THE ATMOSPHERE 36 

many places, so that the distribution of temperature all 
over the world, except in the two frigid zones, is fairly 
well known. 

The distribution of mean annual temperatures for the 
year is shown by isotherms on the chart of the world, 
Figure 12, which is therefore called a chart of annual iso- 
therms. A line drawn near the earth's equator, through 
the middle of the belt of greatest heat, is called the heat 
equator, the average temperature of which is about 80°. 
From the heat equator the temperature decreases toward 
each pole at the rate of about one degree of the Fahrenheit 
thermometer scale to a degree of latitude. 

In the southern hemisphere the isotherms are nearly 
parallel to the latitude circles ; this is because the oceans 
there are so little interrupted by land. 

In the northern hemisphere the isotherms are much 
more irregular, because the oceans are here interrupted 
by broad continents, and the temperatures on lands and 
seas are often unlike in the same latitude. 

Exercise. AVhat parts of the lands and oceans have a mean 
annual temperature above 70°? above 80°? What is the general 
path of the isotherm of zero in the northern hemisphere ? Estimate 
from the chart the mean annual temperature of your home ; of Lon- 
don; of Cape of Good Hope. 

28. „ Circulation of the Atmosphere. — Movements of the 
atmosphere are usually caused by differences of tempera- 
ture. For example, a movement of air will take place 
between two rooms, one warm and the other cold, if a door 
is opened between them. The cold air is heavier than the 
warm air. Cold air Mali therefore creep into the lower 



36 ELEMENTARY PHYSICAL GEOGRAPHY 

part of the warm room, while the light warm air spreads 
into the upper part of the cold loom. The movement may 
be shown by the drift of smoke from a smoldering match. 
If the cold air is warmed as it enters the warm room, and 
the warm air is cooled as it enters the cold room, the 
movement will continue indefinitely, the air going roimd 
and round in a circuit. Such a movement is called a 
circulation. It is also called a convectional circulation, 
because heat and cold are conveyed by the movement that 
is excited by differences of temperature. 

In the same way the cold air of the polar regions, being 
heavier than the warm air of the torrid zone, continually 
tends to creep under it, thus forming convectional air cur- 
rents in the lower atmosphere, which we know as winds. 
The warm air, being slowly raised all aromid the equatorial 
belt, tends to overflov/ north and south toward the poles, 
forming convectional air currents at a great height in the 
atmosphere. 

The lower winds approaching the equator where sun- 
shine is strong are warmed ; thus their air is expanded 
and made lighter, so that it is in tuni slowly raised over 
the equatorial belt to form the overflow toward the poles. 
The upper currents, flowing toward the poles, where sun- 
shine is weak, are slowly cooled; hence their, air settles 
down to lower levels and forms the currents returning 
toward the equator. A permanent interchanging move- 
ment or circulation is thus established between the Avarmer 
and colder parts of the earth. It must continue as long as 
the sun warms the equatorial more than the polar regions. 
On account of the earth's rotation the air does not move 



tup: atmosphere 37 

directly north and south, but is turned obliquely toward 
the east or west. (See page 85.) 

Changes of temperature in the circulating atmosphere are 
produced not only during movements toward or from the 
equatorial belt, Init also during the ascent or descent of the 
air currents. As the warm air rises the pressure of the over- 
lying atmospliere upon it is less and less ; the rising air 
therefore expands, and in so domg it is cooled ; hence even 
over the torrid zone the upper atmosphere is cold. On the 
other hand, as the descending air in higher latitudes sinks 
to lower levels a greater and greater amount of air rests 
upon it ; it is thus compressed and warmed. The descent 
of air from a great altitude is therefore not a cause of cold, 
for the air is warmed by compression as it comes down. 

Changes of temperature of this kind will later be seen 
to be of importance in producing and in dissolving rain 
clouds. Illustrations of such changes may be found in a 
small way by noting the coolness of the air that expands as 
it flows out of a bicycle tire when the valve is opened, and 
the warmth of an air pump in Avhich air has been com- 
pressed in order to force it into a tire. 

The most general movements of the atmosphere thus 
established on a planet like the earth may be called the 
planetary circulation ; the lower members of this circula- 
tion are the planetary winds. The surface wmds move 
much slower than the upper currents, on account of fric- 
tion mth the earth's surface. 

29. Observation of Winds. — The direction of the wind 
is determined by a vane or arrow, turning easily on a 



38 



ELEMENTARY PHYSICAL GEOGRAPHY 



vertical axis and freely exposed, as on a spire or high pole, 
to the movement of the air. The wind is named after the 
point of the compass from which it blows. 

The strength of the wmd may be described as light, mod- 
erate, strong (twenty miles an hour), fresh gale, whole gale, 
hurricane (seventy-five or more miles an hour) ; or it may be 

determined in miles 
per hour by an anemo- 
meter (wind measure) 
turning on a vertical 
axis, as in Figure 13. 

Describe the arrange- 
ment of the cups on the 
arms of this instrument. 
Which way will the arms turn 
when the Mind blows ? Why ? 

A pointer on a small dial, 
connected with the axis of 
the turning arms by cog- 
wheels, indicates the move- 
ment of the wind in miles 
per hour. 
The surface wind on the uneven lands seldom blows in 
straight lines with uniform velocity. It usually rolls and 
whirls, now faster, now slower. 




Fig. 13. Anemometer 



30. RainfaU. — Water is evaporated from the ocean 
surface, especially from its warmer parts, and the invisible 
vapor thus formed mixes with the air and is carried about 
m the Avinds. When the moist air is sufficientlv cooled 



THE ATMOSPHERE 39 

the vapor in it is condensed into minute water drops or 
snow crystals, and the air becomes cloudy. If the cooling 
continues still further, rain or snow may fall. The vapor 
may thus be returned directly to the oceans, or it may fall 
upon the lands, whence it returns to the oceans in streams 
and rivers. In this way there is a circulation of water 
through the atmosphere, from the ocean and back again. 

The processes by which the air is cooled are nearly 
always connected with its movements. Hence the general 
distribution of rainfall will be referred to in the following 
account of the winds, while a fuller account of clouds, rain, 
and snow will be given farther on. 

31. Planetary Winds. — The most important members 
of the planetary winds are the trade winds and the pre- 
vailing westerlies. 

The trade winds blow with much regularity from about 
latitude 28® N. and S. obliquely toward a belt of low atmos- 
pheric pressure around the equator, from the northeast 
in the northern hemisphere, and from the southeast in 
the southern. The prevailing westerly winds blow from 
a westerly source, "but usually with a slight inclination 
toward the pole, over the greater part of the temperate 
zones ; they form great spiral whirls around regions of low 
pressure in the high latitudes of each hemisphere. These 
winds are made irregular by the occurrence of many 
smaller whirls, about 1000 miles in diameter, which drift 
eastward with the general movement of the atmosphere 
in middle latitudes. The winds of tlie polar regions are 
little known. 



40 



ELEMENTARY PHYSICAL GEOGRAPHY 




Narrow belts of light variable winds and frequent calms 
lie between the several belts of steadier winds ; in these 
belts of light winds the pressure of the atmosphere is so 
nearly uniform that the air is not pushed steadily in any 

direction. All these mem- 
bers of the planetary circu- 
lation are better defined over 
the oceans tlian on the lands. 



Point out and name the several 
members of the planetary circula- 
tion in Figure 14. In what 
directions do their winds blow? 
Between what latitudes do they 
occur? 



The trade winds are so 

Fig. 14. The Planetary Circulation ^^ -i £ ,i 

of the Atmosphere ^'^l^^d from the constancy 

with which they follow their 

course, the word trade formerly having meant "steady." 

• They warm slowly as they approach the heat equator. 

Their velocity at sea is from ten to thirty miles an hour. 

They give fair weather, seldom interrupted by storms. 

When sailing vessels enter the trade-wind belt they may 
count upon making good headway. If sailing with the 
winds, extra sails ai-e often rigged out on the ends of the 
yards, and thus aided by a broadened stretch of canvas 
the vessels speed along day and night. 

Coasts upon wliich the trade winds blow are usually 
beaten with lieavy surf, so that landing is difficult, except 
jin well-protected harbors. This is the ease on the north- 
east side of the Windward islands in the Lesser Antilles. 



THE ATMOSPHERE 41 

Lowlands over which the trade winds blow are made 
desert by the drying action of their warming air; for as 
the winds become warmer they take up any moisture that 
they find instead of giving up what they have. The Afri- 
can Sahara and the central Australian deserts are thus 
explained : it is entirely on account of their dryness and 
not because of the infertility of their soils that these 
regions are barren. 

Where the trade winds encounter mountain ranges they 
are forced to ascend the side on which the}^ approach (the 
windward side). As they rise the air expands and cools ; 
as the air cools some of the invisible vapor that it contains 
is condensed into minute drops of water ; thus the ascend- 
ing air becomes cloudy and rainy. The eastern slope of 
the Andes, about the headwaters of the Amazon, the 
mountains along the east coast of Brazil under the south- 
east trades, and the eastern slopes of the highlands of 
Mexico and Central America under the northeast trades 
thus receive a good amount of rainfall (80 to 100 inches a 
year). All these mountain slopes bear heavy forests. 

The further slope of tlie mountains, where the winds 
descend (the leeward side), is relatively dry and barren, 
because as the air descends it is compressed by the weight 
of the air that follows upon it; as it is compressed it is 
warmed, and as it warms it holds all the vapor that it has 
and eagerly takes up any vapor it can get from the ground 
over which it blows. This is especially noticeable on the 
western side of the Peruvian Andes, where much of the 
land is a desert in spite of being near the ocean. 

Even in the Saliara the few mountains that interrupt 



42 



ELEMENTARY PHYSICAL GEOGRAPHY 



the general surface receive a sufficient rainfall to permit 
tree growth ; but the streams supplied on the mountain 
sides wither away after descending to the desert below. 

The prevailing westerlies are much less regular than the 
trades. They may weaken to less than ten miles an hour, 
or strengthen to gales of sixty or more miles an hour. 

They often shift 




from their general 
course to take part 
in the drifting spiral 
movements indicated 
in the temperate lati- 
tudes of Figure 14. 
It is chiefly to these 
great whirllike 
movements that the 
frequent changes of 
weather in temper- 
ate latitudes are due. 
The area of the 
United States lies 
almost entirely 
within the belt of the prevailing westerlies. If the wind is 
observed at noon every day for a month or two, a westerly 
direction will be found more common than an easterly. If 
the drift of clouds is observed, the general movement of 
the atmospheric currents from the western toward the 
eastern side of the sky is very noticeable. Variations from 
these prevalent directions are generally due to the drifting 
spiral movements. 



Fig. 15. Wet-Weather Streams of the Tarso 
Mountains, Sahara. Locate these mountains 
on the chart of mean annual temperatures, 
Figure 12, by the latitude and longitude here 
given 



THE ATMOSPPIERK 43 

The lands under the westerly winds are generally well 
watered if they do not lie too far from the oceans ; the con- 
tinental interiors are comparatively dry. Abundant rain- 
fall is received on the mountainous Pacific slopes of North 
and South America in middle latitudes, but the opposite 
slopes are drier. In these latitudes the western (wind- 
ward) slope of the mountains is heavily forested, while the 
eastern (leeward) slope has an open tree growth or none. 
The distribution of forests over the great American moun- 
tain system thus gives striking illustration of the relation 
of timber supply to winds, land forms, and rainfall. 

The belt of calms and light breezes in the neighborhood 
of the equator, between the trade winds, is called the 
equatorial calm belt ; that part of the belt which lies on 
the oceans is known to sailors as the doldrums. The air 
in the doldrums is moist and sultry, for the warm inflow- 
ing trade winds gather much water vapor as they blow 
over the ocean. The sky is prevailingly cloudy; rain 
falls every day or two, especially in the late afternoon or 
night. The lands are heavily forested under this warm 
and moist belt, and agriculture is diificult from the very 
luxuriance of vegetation. 

Sailing vessels bound across the equator are frequently 
becalmed for several days in the doldrums ; there they lie 
idle, rocking very gently to and fro in the long flat swell 
that sweeps across the glassy waters. They must then 
take advantage of every light breeze to push onward and 
reach the trade winds beyond. The dull sky, the sultry 
air, and the glassy sea make the delay all the more 
vexatious. 



44 ELEMENTARY PHYSICAL GEOGRAPHY 

The rain of the doldi'ums results from the slow ascent of 
the warm moist air supplied by the inflowing trade winds. 
The lower air is raised to greater and greater height by the 
inflow of more air beneath from both sides ; it expands as 
it rises, and cools as it expands ; the vapor in the air is 
then condensed into cloud particles, tlie clouds become 
heavier and heavier and give forth plentiful rain ; the air 
from which the rain has fallen continues to rise and at 
last overflows aloft and thus supplies the upper currents 
that move obliquely toward the poles. Violent thundfer- 
storms are frequently formed in the great cloud masses of 
the calm belt. 

The ill-defined belts of light breezes and occasional 
calms lying between the trades and the prevailing wester- 
lies in each hemisphere are known as the liorse latitudes. 
Their light winds usually blow obliquely outward on both 
sides ; hence the air here must slowly descend from the 
upper currents to supply the ontflcrwing breezes. As the 
air slowly settles down it is compressed by the weight of 
that which rolls in on top of it ; as it is compressed it is 
warmed, and as it is warmed any clouds that it may have 
contained are dissolved ; hence clear fair weather is preva- 
lent in this belt. 

32. Whirls of the Westerly Winds. — The irregular 
winds by which the prevailing westerlies are so often 
interrupted sometimes have an inward, sometimes an out- 
ward, spiraling movement, as in Figure 16. They are like 
great slow-turning whirls from 500 to 1000 miles in diame- 
ter ; they may be compared to eddies in streams of water. 



THE ATMOSPHERE 



46 



When blowing outward the air slowly descends from 
aloft ; the winds are light and the weather is fair, for the 
reasons already given for the fair weather of the horse 
latitudes. When blowing inward the air slowly ascends, 
and the weather is cloudy and wet, for the reasons given in 
explaining the doldrums. Here the winds may gain a 
stormy strength, fifty to eighty miles an hour on land and 
sometimes over one hun- 
dred rniles an hour at sea. 



Exercise. Locate the cen- 
ters of the two whirls shown 
in Figure 16. Describe the 
spiral movement of the winds 
with respect to the centers. 
Tu which whirl does the turn- 
ing around the center agree 
^\■ith the turning of the hands 
of the clock? Which whirl 
should have low pressure? 

Which one fair weather? „ -,,■ r i i r^, , i ^x-^ ■ ^ 

Fig. K). Inward and Outward ^\ lurls 

Both classes of whirls 
travel from 500 to 1000 miles a day in an easterly direc- 
tion, with the general drift of the atmosphere in temperate 
latitudes. Changes of weather are caused by their pas- 
sage. The whirls may strengthen and increase in area for 
a time, then weaken and fade away ; their duration being 
from a few days to two or three weeks, and their distance 
of travel from 5000 to 15,000 miles or more. The direc- 
tion in which the whirls turn in the northern hemisphere 
is opposite to that in the southern ; that is, the outflowing 
spirals turn clockwise in the northern hemisphere, as in 




46 ELEMENTARY PHYSICAL GEOGRAPHY 

Figure 16, and counter-clockwise in the southern hemi- 
sphere. How do the inflowing spirals turn in the two 
hemispheres ? 

The pressure of the atmosphere, as shown by the barom- 
eter, is less than usual about the central part of the stormy- 
inward whirls, and greater than usual in the fair-weather 
outward whirls. Hence they are often called low-pressure 
and high-pressure areas. They have also been named 
cyclonic and anticyclonic areas from the curving move- 
ment of their winds. They will be further described in 
the section on weather. 

33. Seasons and Zones. — As the earth moves around 
the sun there are six months in each year (March 21 
to September 22) in which the northern hemisphere is 
inclined somewhat toward the sun, so that it has longer 
days and stronger sunshine than the southern, which is at 
the same time inclined somewhat away from the sun, as in 
Figure 17. 

In this condition the gain of heat in the northern hemi- 
sphere by the absorption of the strong sunshine during the 
long days is greater than the loss of heat by radiation dur- 
ing the short nights ; hence the temperature there rises 
above the mean of the year. But in the southern hemi- 
sphere the loss of heat by radiation during the long 
nights is greater than the gain by absorption of weak sun- 
shine during the short days ; hence the temperature there 
falls below the mean of the year. During these months 
the northern may be called the sunnner hemisphere, and 
the southern the winter hemisphere. 



THE ATINIOSPHERE 



47 



During the other six months of the year (September 22 
to March 21) the southern hemisphere is inclined toward 
the sun, and the northern away from it, so that the above 




N " 



Fig. 17. Monthly Positions of the Earth with Respect to the Sun 



conditions are reversed. The southern is then the sum- 
mer hemisphere, and the northern the winter hemisphere. 
In both hemispheres the succession of higher and lower 
temperatures during the year produces the change of 



48 ELEMENTARY PHYSICAL GEOGRAPHY 



seasons. The winter months in the northern hemisphere 
are December, January, and February (these being the 
summer months of the southern hemisphere) ; the spring 
months are March, April, and May ; the summer months, 
June, July, and August ; the autumn or fall months, 
September, October, and November. 

The zones maybe defined b}^ means of Figui-e 17 as fol- 
lows : In the torrid zone, from 231-° N. to 231-° S.^ every 
point receives vertical sunshine sometime in the year ; 
here the days do not vary much from twelve hours in 
length. In the frigid zone, extending 23^° from each 
pole, there is at least one day in the year when the sun 
does not rise and another when it does not set ; here the 
days vary greatly in length. The temperate zones occupy 
the space between the torrid and the frigid zones (231° 
to QQ^°), north and south latitude ; here no place has ver- 
tical sunshine on any day, and no day passes without a 
sunrise and a sunset. 

If zones are limited by the mean annual isotherms of 
70° and 30°, their borders are much more irregular than 
when limited by sunshine. 

34. Observations of the Sun. — Records of thermometer 
readings during the school year should be used to show 
the general fall of temperature to midwinter, and the 
general rise from midwinter to midsummer. These 
changes of temperature should be connected with the 
changes in the apparent movement of the sun. In late 
December the sun rises south of east and sets south of 
west ; at midday it reaches but a moderate altitude above 



:1 



THE ATMOSPHERE 49 

the southern horizon ; at this time the dnration of daylight 
is less than twelve hours and the strength of the sunshine 
is reduced. In late June these conditions are all reversed. 
The low temperature of winter is thus seen to depend on 
the weak sunshine of short days, and the high temperature 
of summer on the strong sunshine of long days. The ris- 
ing temperature through spring results from the strength- 
ening of simshine in the lengthening days ; the falling 
temperature of autumn, from the weakening sunshine in 
the shortening days. (See Supplement.) 

35. Change of Temperature with the Seasons. — An 

observer at any one place notes the familiar succession of 
the seasons during the course of the year. A better 
understanding of the ■ meaning of the seasons may be 
gained if the earth as a whole is considered, as on the 
above charts. It is then seen that for a time the heat 
equator moves a moderate distance from the geographic 
equator into the summer hemisphere, while the high tem- 
peratures of the torrid zone advance into the temperate 
zone, and the rigor of polar cold is somewhat lessened ; in 
the other hemisphere the polar cold is extreme, low tem- 
peratures advance over the temperate zone, and the heat 
on the border of the torrid zone is decreased. 

In the next half year the heat equator moves slowly 
back and crosses the geographic equator, and all these con- 
ditions are reversed. The year, or period in which the 
earth revolves around the sun and in which the change of 
seasons therefore take place, thus comes to be a natural 
measure of time. 



50 ELEMENTARY PHYSICAL GEOGRAPHY 

36. January and July Isotherms. — The general distri- 
bution of mean temperatures for January and for July is 
shown in charts of monthly isotherms, Figures 18 and 19, 
on which the following exercise may be based. 

Exercise. In which summer hemisphere does the heat equator 
stand farther from the geographic equator ? Does the heat equator 
stand farther from the geographic equator on the oceans or on the 
lands? Where do midsummer temperatures of more than 90° 
occur? In which hemisphere do they cover the largest area? What 
is the lowest mean temperature in January ? Where does it occur ? 

About how much difference is there between January and July 
temperatures in latitude 40° S. ? Where in latitude 40° N. is there 
a strong difference between January and July temperatures ? 

37. Mean Annual Range of Temperature. — The average 
change of temperature with the seasons may be best 
studied by taking the difference between the mean temper- 
atures of January and July. This difference is called the 
mean annual range of temperature. It is shown for the dif- 
ferent parts of the world in Figure 20. The range is gen- 
erally less than 10° over the torrid oceans and less than 
20° over most of the temperate oceans. On land the range 
increases. Places in the interior of continents have a much 
stronger range than those on continental borders or islands. 

Central Australia and the interior of the Sahara have a 
range of over 30°. Over most of the United States the 
range is from 30° to 60°. Over a belt of land from Hudson 
bay into Alaska the range is more than 80°. Over the 
greater part of Europe- Asia the range exceeds 40°. 

In regions of the greatest range the winters are so cold 
that the ground is frozen to a depth of 100 feet or more. 



120 180 160 I2U 80 



40 30 120 




«;^»^ 



~no 160 160 120 



40 80 120 



Fig. 18. Chart of Mean Temperatures for January 




Fig. 1!). Chart of Mean Temperatures for July 



THE ATiMOSPIlERE 



61 



In winter ice is so hard that the runner of a skate does 
not hold upon it; wood is too hard to be chopped with 
an ax. In summer thawing reaches onl}^ a few feet 
below the surface. Trees gain only a stunted growth .or 
are altogether wanting. 

Compare the annual range on the western and eastern 
coasts of the continents in temperate latitudes. On which 




Fig. 20. Chart of Annual Range of Teniperatiire 



coast is the range of less amount ? The difference of range 
is due to the prevailing westerly winds, which carry the 
nearly uniform conditions of the ocean on to the western 
coasts, and the changing conditions of the continental 
interior out to the eastern coast. 

Exercise. Wliere is the greatest annual range? What is its 
amount? Coiaipare the annual range of Labrador and England, of 
Virginia and Spain, of Japan and California. 



52 - ELEMENTARY PHYSICAL GEOGRAPHY 

The annual changes of temperature are much more dis- 
tinct in the northern hemisphere, where there is much 
land, than in the southern, where there is much ocean. 
This is because the land surface changes its temperature 
more easily than the ocean surface, and therefore the air 
over the land becomes hot in summer and cold in winter. 
The change of seasons in the north temperate zone, 
especially on the lands, is much stronger than in the south 
temperate zone. This is because the northern continents 
are broad in temperate latitudes, while the southern are 
relatively narrow. 

Exercise. In Figure 20 follow the latitude circle of 40° or .50° N. 
around the earth. For how many degrees of longitude does it lie 
on the continents? How many on the oceans? Do the same for 
latitudes 40° or 50° S. Compare the results. 

Winter and summer are not very different over the great 
oceans of the south temperate zones, where the weather 
is rather uniformly chill and damp, or inclement, all the 
year round. This is because water is slow to change its 
temperature ; the ocean waters and the air over them suffer 
small changes of temperature during the year. 

In the temperate zone the summer half year is the time 
of plant growth, and is therefore the season of greater 
activity in all industries immediately connected with agri- 
culture. One of the most interesting consequences of the 
advance of spring and summer temperatures into higher 
latitudes is the northward passage of migratory birds, 
familiar to every lover of outdoor nature. The approach 
of winter is accompanied by the return of the birds to 
warmer latitudes. 



THE ATMOSPHERE 



53 



38. Terrestrial Winds. — The strength of the planetary 
circulation and the boundaries of its wind belts vary with 
the seasons. Thus modified, the winds may be called 
terrestrial, as belonging to the earth in particular with its 
winters and summers, instead of to the other planets which 
may not have seasons like ours. 




Fig. 21. Diagrams of Terrestrial Winds for January and July 



Figure 21 gives a general scheme of the winds for January and 
JuTy, without considering the irregular winds produced by the 
continents and their mountain ranges. The heavier lines show 
the stronger winds. In which month are the winds strongest in 
the northern hemisphere? In what season is this? Answer the 
same questions for the summer hemisphere. In what season are the 
prevailing westerlies most interrupted by spiraling winds (cyclones 
and anticyclones)? 

Examine the isotherms in the northern hemisphere for January 
and July, Figures 18 and 19. In which month are the lines closer 
together? How can you tell from this in which month there is the 
greatest difference of temperature between the torrid zone and the 
Arctic regions? In which month would you exp)ect the general 



54 



p:lementary physical geography 



circulation in the northern hemis})here to be the stronger? AVhy? 
Answer the same questions for the southern hemisphere. Compare 
the results for the two hemispheres. 

It is thus seen that in winter the difference of tempera- 
ture between the equator and high latitudes is strength- 
ened. As the general circulation of the atmosphere 
depends on this difference, the winds will generally be 







Fig. 22. Winds of January- 
stronger in winter than in summer. This is especially 
true of the prevailing westerlies and their spiraling 
cyclonic winds in the northern hemisphere ; they fre- 
quently become stormy in winter, while they are rela- 
tively light in summer. In the southern hemisphere 
these changes are less marked. Why so? 

Examine in Figure 21 the belts of light breezes and occasional 
calms between the trades and the westei'lies. What is the name of 
these belts? Compare their positions in January and July. AVhat 



TPIE ATMOSPHERE 



55 



is the name of the belt of calms and light breezes between the trade 
winds ? How does its position change with the seasons ? 

The horse latitudes and equatorial calms are much less 
regular in reality than they are represented in Figure 21, 
on account of the irregular outline and form of the lands. 
A better illustration of the prevailing winds for January 
and for July is given in Figures 22 and 23. 




Fig. 23. Winds of July 

The light and irregular winds of the horse latitudes 
migrate toward the equator in the winter of their hemi- 
sphere, and toward the pole in the summer ; these belts of 
migration are known as the northern and southern subtropi- 
cal belts (ST, Figure 21). Any country over which a sub- 
tropical belt is stretched will have the westerlies and their 
rainy storms in winter and the drying trades in summer. 
This is the case with southern California and the Mediter- 
ranean countries of southern Europe and northern Africa, as 



56 ELEMENTARY PHYSICAL GEOGRAPHY 

well as with central Chile, southern Africa, and south- 
ern Australia. These countries are said to have, a sub- 
tropical climate. In what months will they have their 
rainy season? 

As -countries in the subtropical belts are dry in the 
growing season, agriculture there generally requires the 
aid of irrigation (watering the fields by canals led from 
streams or reservoirs). 

Like the calms of the horse latitudes, the calms and 
rains of the doldrums also migrate north and south dur- 
ing the year. The belt of winds and rainfall thus con- 
trolled forms the subequatorial belt (SQ, Figure 21). The 
migration of these three belts follows the migration of 
the sun. 

The plains of the Orinoco in Venezuela, north of 
the equator, receive a plentiful rainfall in July and 
August, but in December and January they are relatively 
dry. In the wet season cattle find abundant pasture 
on the plains, but in the dry season they are driven 
into the valleys. On the plains between the headwaters 
of the Amazon and the Parana, south of the equator, the 
months of wet and dry seasons are reversed from those 
of Venezuela. 

The western Sahara, between the reach of the subtropical 
(winter) rains on the north and the subequatorial (summer) 
rains on the south, gives no important river to the Atlantic 
along a thousand miles of coast line. The rise of the 
Nile in Egypt from June to September results from the 
northward advance of the equatorial rains over the upper 
part of this river basin, as in Figure 23. 



THE ATMOSPHERE 



57 




39. Monsoons. — In the belt over which the equatorial 
calms move north and south during the year the trade 
winds change their direction in the warmer and cooler half 
years. Winds of this kind are called monsoons. 

How do the winds blow in the northern half of the subequato- 
rial belt (S'Q, Figure 21) 
in January? in July? 
how in the southern 
half? 

What parts of the 
equator are crossed by 
the extended northeast 
trades in January, Fig- 
ure 22 ? by the ex- 
tended southeast trades 
in July, Figure 23 ? 
Where do these ex- 
tended winds cover the 
greatest area? 

Note in Figure 24 thi_^ 
change in the direction 
of the northeast trades 
in January as they cross 
the geographical equa- 
tor and enter the south- 
ern hemisphere on their 
way to the calm belt. 
What is the direction 
of the wind in the same 

part of the southern hemisphere in July? Note the corresponding 
change in the extended southeast trades for July in Figure 25. 

The reason for this change of direction as the winds cross 
the equator is found in the earth's rotation, on account of 



Fig. 24. January Monsoons in Indian Ocean 




Fig. 25. July Monsoons in Indian Ocean 



58 ELEMENTARY PHYSICAL GEOGRAPHY 

which all winds in the northern hemisphere tend to turn to 
the right, and in the southern hemisphere to the left. On 
account of the irregular distribution of land and water mon- 
soons are not evenly developed all around the equator. 

The monsoons of the Indian ocean are the most remark- 
able of the world. In January a belt of northwest mon- 
soon winds is developed for about ten degrees south of the 
equator, as in Figure 24. In July, when the heat equator 
has shifted far northward to the border of Asia, a broader 
belt of southwest monsoon winds is developed north of 
the equator, as in Figure 25. 

The primitive sailing vessels of the Indian ocean in 
earlier centuries, poorly adapted for sailing against the 
wind, made voyages only as the monsoons favored their 
courses, going outward from India to Africa in one half 
year and returning in the next. 

The east coast of the Malay peninsula is beaten by heavy 
surf under the northeast monsoon, and then the native fish- 
ermen stay ashore. But under the southwest monsoon, 
an offshore wind, the water is comparatively smooth, and 
large fleets of fishing boats put out to sea with their 
palm-leaf sails. 

In what months would the events described in the two preceding 
paragraphs be expected ? -. 

40. Winds of the Continents. — As the air over the con- 
tinents is warmer than that over the neighboring oceans 
in summer and colder in winter, the winds tend to blow 
inward toward continental centers in summer and outward 
from them in winter, 



THE ATMOSPHERE 59 

111 the north temperate zone the cold land winds of 
winter tend outward toward the sea, and the far inland 
regions have much clear and dry weather. In summer 
the warm and moist sea winds tend inward toward the 
still warmer lands, and the interior parts of the large con- 
tinents then have a greater abundance of clouds and rain. 

The general circulation of the atmosphere is much com- 
plicated by this outward and inward tendency of the winds 
over the continents, as may be seen by comparing the 
winds of January and July over Asia, Figures 22 and 23, 
with the winds of corresponding latitudes in Figure 21. 
The regular belts of winds in the latter figure are much 
broken up, especially in the northern hemisphere. 

41. Winds on Land. — The lower winds are generally 
not so strong or so regular on the uneven lands as on the 
level seas, although the upper currents over the lands still 
flow rapidly. In valleys the winds are much influenced 
by the direction of the inclosing slopes. Hence observers 
living in deep valleys may often determine the general 
direction of the winds better by watching the drift of the 
clouds than by noting the position of their wind vanes. 

The air over the lands is cooler and therefore heavier 
than that over the sea at night, but warmer and lighter by 
day. Hence around the border of the lands the wind 
tends to blow alternately offshore at night and onshore by 
day for a short distance from the coast, such winds being 
kno^vn as land and sea breezes. 

On the coasts in the torrid zone the sea breeze is wel- 
come, as it tempers the excessive heat of the day on land. 



60 ELEMENTARY PHYSICAL GEOGRAPHY 

The same is true of sviramer weather in tlie temperate 
zone. On the coast of Peru the fishermen sail offshore in 
the early morning with the land breeze, and return in the 
afternoon with the sea breeze. 

42. Daytime Winds In fair, warm weather the lower 

air lying on the land becomes unduly heated by day, as 
compared with the overlying air. The warmer lower air 
then rises and the cooler upper air descends, this be'ing a, 
small example of convectional circulation. It is like the 
movement of water in a kettle that is heated at the 
bottom. 

The faster-moving currents from aloft are thus brought 
down to the surface. Hence on lands the winds of fair 
weather in the daytime are commonly stronger than those 
of the night. This is prevailingly the case tlirough the 
year on torrid lands ; on the temperate lands it is common 
during summer weather, but is less noticed in winter. 
Why does no such daily change in the strength of the 
wind occur at sea? 

43. Humidity. — The condition of the atmosphere as to 
the water vapor that it contains is expressed by the term 
humidity. When the air contains much vapor and feels 
damp the humidity is said to be high. W lien it con- 
tains little vapor and feels dry the humidity is low. The 
higher the temperature of the air, the greater the amount 
of vapor it may contain. When as much vapor is present 
as is possible at a given temperature the air is said to be 
in the state of saturation. The lower air over the ocean 
is usually almost saturated ; in the doldrums tlie humidity 



THE ATMOSPHERE 61 

is always high. Far inland, in the desert regions of con- 
tinents, the air may contain very little vapor; here the 
humidity is low. Dry air is more agreeable than damp, 
because it allows active evaporation from the skin. Cold 
damp air is chilly and " penetrating." Warm damp air is 
sultry and "close." 

44. Dew and Frost. — Dew is a deposit of moisture on 
the gromid, or on loose objects like leaves and sticks lying 
on the ground. It is formed when the ground is cooled 
at night by radiation ; then the air near it is chilled by 
conduction, and some of the water vapor in the air is 
changed to the liquid form. The temperature at which 
dew begms to be formed in cooling air is called the dew- 
point. 

Exercise. The dew-point may be determined by experiment as 
follows: Half fill a tin cui3 with water whose temperature is about 
like that of the air. Then slowly pour in ice water, stii-ring it with 
a thermometer. As the cup is cooled the air next to it is cooled 
also. As the air is cooled the vapor that it contains will more and 
more nearly saturate it. When the outer surface of the cup is first 
clouded by a deposit of moisture the air next to it has just passed 
the condition of saturation, and the temperature of the water gives a 
close indication of the dew-jjoint. If ice is added so as to make the 
water still colder, more and more vapor will be condensed on the 
cup, the air constantly being saturated with the vapor that remains 
in it as its temperature falls. 

When moisture is condensed upon the ground at tem- 
peratures beloAV the freezing point it forms frost. Thus 
frost on the gromid corresponds to snow m the air, and 
dew con-esponds to rain. 



62 ELEMENTARY PHYSICAL GEOGRAPHY 

Dew and frost are in part supplied, from water vapor in 
the air that lies near the ground, in part by vapor that rises 
through the soil from its deeper and moister parts. In the 
daytime the vapor from the soil escapes into the warm air ; 
but at night, when the ground is colder at the surface than 
beneath,, the rising vapor is condensed.^ Dewdrops found 
on the blades of grass and on the livmg leaves of plants 
close to the ground are in large part supplied by the water 
that the plants bring up from the ground through the 
roots. In the daytime the moisture evaporates from the 
leaves, but at night it may collect upon them in drops. 

• At night, when the air is calm and clear, the ground is 
cooled by losing its heat to cold outer space ; the quiet 
lower air is then chilled, because it lies on the cooled 
ground, and dew (or frost) is formed. When the wind is 
blowing the lower air is constantly changed and none of 
it is much chilled; when the sky is cloudy at night the 
gromrd cools but little ; hence on windy or cloudy nights 
little or no dew (or frost) is formed. 

45. Clouds, Fog, and Mist. — The different processes by 
Avhich water vapor is condensed ^ in the atmosphere pro- 
duce clouds of many different forms. It has been explained 
that in daytime of fair summer weather the lower air tends 
to rise in convectional currents. The ascending air currents 

1 It should be noticed that the term condensation, when applied to vapor, 
refers to its change from the gaseous to the liquid (or solid) state, and not' 
to its compression, as vapor, into a smaller volume. Hence condensation 
of vapor may take place while the air with which it is mixed is expanding, 
provided that the expansion produces sufficient cooling to lower the tem- 
perature below the dew-point. 




Platk III. B. Cirrus Clouds 




rL.VTK III. A. Cuiiuilus Clouds 



THE ATMOSPHERE 63 

expand and cool as they rise, and, if their ascent is great 
enough, some of their vapor is condensed, forming round- 
topped clouds, brilliant white in strong sunshine, as in 
Plate III, A ; the air within the clouds is all saturated 
by the vapor it still contains. The clouds are of unequal 
size, but have their bases at about the same height {com- 
monly one fourth to one half of a mile), and all drift 
along with the speed of the currents in which they are 
formed. Their rapid motion can be recognized by watch- 
ing their shadows pass across a field ; they nearly always 
drift eastward in the United States, being borne in the 
prevailing westerly winds of middle latitudes. 

Clouds of this kind are called cumulus (heap) clouds. 
They usually begin to form in the warming morning hours 
of fair weather, but dissolve and disappear in the late 
afternoon, when sunshine weakens, the ground cools, and 
convection ceases. 

It is usually the case that the great cyclonic storms of 
the westerly winds are preceded by long filmy or feathery 
strips of pale whitish cloud, as in Plate III, B. Clouds of 
this kind are formed at a height of several miles, in the air 
currents that flow out and forward from the upper part of 
the storm. They are called cirrus (curl) clouds. They con- 
sist of minute ice crystals, -because the moisture forming 
them has been condensed in the cold upper air at tempera- 
tures below the freezing point. Sometimes the cirrus is 
spread out in a thin sheet called cirro-stratus. When the 
sun or moon is seen through a cirro-stratus a large ring 
faintly colored with red on the inside is seen around the 
luminary. Such a ring is called a halo ; it is formed by 



64 ELEMENTARY PHYSICAL GEOGRAPHY 

the bending (refraction) of the light in passing through the 
ice crystals. Halos are common and brilliant in the polar 
regions. 

In the central parts of the great whirling cyclonic storms 
heavy dull-gray cloud sheets of great size are formed 
at a moderate height above the earth's surface by the 
gradual cooling of the inflowing winds. Clouds of this 
kind, from which rain or snow falls, are called alto-nimbus 
and nimbus. A nimbus cloud is shown on the right side 
of Plate IV. As with other clouds, the air withm the 
nimbus is constantly saturated. These clouds often cover 
the area of several states at once, and they may hide 
the sun and stars for several days at a time, yielding- 
plentiful rain or snow before they drift away eastward 
and reveal the clear sky again in fair weather. They are 
especially large and heavy in winter, when the westerly 
winds and their storms are strongest. When the sun or 
moon is seen through the fragments of nimbus clouds it is 
often closely surrounded by a brilliant glow, called a corona. 

When a cloud is formed at so low a level that it rests 
on the ground or on the sea surface it is called fog. This 
is often the case when moist sea winds of mild temperature 
blow across a colder part of the sea or blow inland over 
snow-covered hills. Fog is often formed in valleys among 
mountains by the coolmg of the lower air at night. Fog 
of this kind usually disappears in the morning sunshine, 
but if very heavy it may not be dissolved by the short and 
weak sunshine of a winter day. 

A slight cooling of damp air may produce a faint cloudi- 
ness, known as mist, much less dense than fog. 



THE ATMOSPHERE 65 

46. Thunderstorms. — When the lower air is warm and 
moist it is apt to rise and form great cumulus clouds from 
ten to fifty miles in length, whose tops may reach heights 
of more than a mile. When the rising movement is active 
and the cloud grows to great size it may often be seen to 
spread out at the top in a cirro-stratus film, and about the 
same time ram falls from its base. If the rain becoines 
heavy, lightning flashes occur, causing peals of thunder; 
hence such storms are called thunderstorms. 

Storms of this kind are common in the cloudy belt of 
the doldrums, where they usually occur in the afternoon 




Fig. 26. A Distant Thunderstorm 

and evenmg. They are also common on the lands in 
periods of hot summer weather. Much of the summer 
rain in the Mississippi valley falls from thunderstorms 
which drift eastward in the afternoon and night at a rate 
of twenty or thirty miles an hour, giving heavy rainfall for 
an hour or two as they pass by. "A violent blast of wind, 
or thunder squall, often rushes forward from beneath the 
front of the cloud mass, raising a cloud of dust before the 
rain arrives. 

During the growth of a thunderstorm cloud the water 
particles in it become charged with electricity. When the 
drops become large enough to fall as rain the electricity 
is discharged from one part of the cloud to another, or from 



66 ELEMENTARY PHYSICAL GEOGRAPHY 

the cloud to the ground, in a great electric spark, or light- 
ning flash. Thunder is the sound caused by the violent 
agitation of the air along the flash. It may be compared 
to the sound caused by snapping a whip. As sound travels 
through the air at the rate of a mile in five seconds, the 
distance of a flash can be determined in miles by counting 
the number of seconds between the lightning and its 
thunder clap and dividing the number by five. The 
" rolling " of thunder is caused partly by the continuous 
arrival of the sound from different parts of a long flash, 
partly by the echoing from clouds or from hills and moun- 
tains. At night the upper clouds of distant thunderstorms 
are illuminated by flashes, commonly called heat lightning, 
too far away for the thunder to be heard. 

An unusually heavy and violent rain, popularly known 
as a cloud-burst, sometimes falls during a thunderstorm 
upon a small district. If on a hillside it may wash away 
the soil, baring the rock beneath. 

47. The Rainbow. — When a thunderstorm passes east- 
ward in the late afternoon a rainbow is usually seen by 
observers on the west of it. The bow is formed by the sun- 
light that is turned back and bent (refracted) by the drops 
that are falling from the rear of the cloud. The center of 
the bow will be directly opposite the sun. Why will a 
rainbow form a half circle at sunset? Why does a rain- 
bow usually show less than a half circle ? A bow forming 
a complete circle might be seen from a balloon. 

48. Tornadoes and Waterspouts. — Violent whirlwinds 
are occasionally formed in thunderstorms. They are seldom 



THE atmospherp: 67 

more than a quarter of a mile in diameter ; they drift along 
with the thunderstorm in which they are formed, usually 
in an easterly direction, passing by in a minute or two. 
Their whirling winds are strong enough to blow down 
trees and overturn buildings. Violent local storms of this 
kind are often called cyclones, or prairie twisters, in the 
Mississippi valley, but the name tornado is to be preferred 
in order to distinguish them from the much larger and less 
violent cyclonic storms. 

When violent whirlwinds of this kind occur over a 
water surface a watery column is formed in their vortex ; 
they are then called waterspouts. Plate IV shows a water- 
spout over Vineyard sound, southeastern Massachusetts, 
as photographed on Aug, 19, 1896. A vessel overtaken 
by such a whirlwind may be suddenly dismasted. 

49. Tropical Cyclones (Hurricanes and Typhoons) ^ — 

Violent storms known as tropical cyclones are occasionally 
developed in the doldrums when the heat equator stands 
farthest from the geographical equator. They appear to 
be, like thunderstorms, due to the inflow, ascent, and out- 
flow of very warm moist air. They grow to be several 
hundred miles in diameter, with violent winds, whirling in 
great spirals around a center of low barometric pressure, 
great cloud sheets, and heavy rains. 

As in the cyclonic storms of temperate latitudes, the 
winds of tropical cyclones turn counter-clockwise in the 
northern and clockwise in the southern hemisphere. As 
tropical cyclones increase in size, they travel slowly (one 
or two hundred miles a day) westward and toward the 



68 



ELEMENTARY PHYSICAL GEOGRAPHY 



temperate zone near the western border of their ocean. In 
a week or ten days they pass from the trade-wind belt into 
the prevailing westerlies. As they enter the temperate 
zone, still increasing in size but usually decreasing in 
violence, their path curves eastward, and they join the 
great procession of cyclonic storms of middle and higher 




Fig. 27. Regions of Tropical Cyclones 

latitudes. The chief regions of these storms are shown 
by dotted areas in Figure 27. 

In the southern hemisphere the doldrums of the Atlantic 
hardly pass south of the equator, on account of the large 
supply of cooled water that comes northward west of 
Africa ; hence no tropical cyclones occur on the Brazilian 
coast. In the western Pacific ocean the doldrums are 
farthest south in February and March, and at that time 
cyclones occur in the region of the Fiji islands. In the 
southern Indian ocean cyclones occur in the same months 
east of Madagascar. 



THE ATMOSPHERE * 69 

I In the northern hemisphere the doldrums are farthest 
north in the western Atlantic and Pacific in August and Sep- 
tember ; cyclones occur in these months in the West Indies, 
where they are commonly called hurricanes, and in the region 
of the Philippmes, where they are known as typhoons. In 
the Indian ocean there are two seasons when the doldrums 
stand over the warm seas between the equator and Asia : 
one in May, as the doldrums are moving north ; one in 
October, when they are moving south ; hence in this ocean 
alone there are two seasons when tropical cyclones occur. 

Formerly much destruction was wrought on vessels at 
sea by the furious winds of tropical cyclones ; but now 
that the season of occurrence, the usual path, and the 
behavior of the winds of hurricanes have been learned, and 
now that vessels are built larger and stronger, losses at sea 
are much less serious than they were a century ago. 

When hurricane winds blow over islands in the torrid 
oceans they may cause much damage to vessels in the 
harbors by driving them ashore, and to settlements by 
destroying the houses and plantations. Cocoanut palms 
may thus be stripped of their leaves, after which the trees 
require a number of years of growth before again bearing 
the fruit of which so many uses are made. 

The great sea floods by which Galveston, Texas, was 
devastated in September, 1900, were caused by the winds 
of a tropical cyclone which brushed the surface waters 
from the Gulf of Mexico into the streets of the city. 
Similar sea floods have repeatedly occurred on the low- 
lands at the head of the Bay of Bengal, drowning many 
thousands of the people. 



70 ELEMENTARY PHYSICAL GEOGRAPHY 

50. Rainf alL — Rain, snow, hail, and sleet are all included 
under the general term rainfall. The explanation already 
given in Section 30 has shown how closely the amount and 
season of rainfall are connected with the circulation of the 
atmosphere. 

Snow occurs when the moisture of the air is condensed 
at temperatures below the freezing point (32°). Snow 
flakes ar6 six-rayed ice crystals of various patterns. Rain 
occurs when the moisture of the atmosphere is condensed 
into drops at temperatures above the freezing point, or 
when the snow flakes of lofty clouds descend into the 
warmer lower atmosphere and melt before reaching the 
ground. Sleet is half-melted snow. 

Hail is a mixture of ice and snow, usually in romided 
pellets, sometimes half an inch, rarely an inch, in diameter. 
It occurs chiefly in summer, when the ascendmg currents 
of lofty thunderstorms carry raindrops so far upward that 
they are frozen and coated with snow before they fall. 
Hailstorms occasionally do much damage to crops and 
buildings. 

Hail should not be confounded with the little pellets of 
nearly transparent ice, properly called frozen rain, caused 
by the fall of raindrops from a cloud whose temperature 
is above 32° through a lower stratum of freezing air. 
Hail occurs chiefly in hot summer weather ; frozen rain 
in winter. 

The amount of rain is determmed by measuring the 
depth of water that is collected in a cylindrical vessel 
having vertical sides, called a rain gauge. The gauge 
should be set in an open space, away from trees and 



THE ATMOSPHERE 71 

buildings. Snow should be melted before it is measured. 
Eight or ten inches of snow correspond to about an inch 
of rainfall. An aiuiual total of eighteen, twenty, or more 
inches is necessary for agriculture, as over the great prairie 
region of the Mississippi and Ohio valleys from the 95th 
meridian eastward. If the annual amount is between 
eighteen and ten inches, agriculture requires irrigation, as 
on a large part of the Great plains east of the Rocky moun- 
tains, and over large areas m the basins of Utah and Nevada ; 
but scattered grass sufficient for cattle ranges may grow in 
such regions. If the annual total is under twelve or ten 
inches, there will not be water enough for irrigation, unless 
it is supplied by rivers that rise in a moister climate, as in 
parts of Arizona and southeastern California. • 

The distribution of the annual rainfall over the world, 
represented in Figure 28, shows that the greater amounts 
(eighty inches or more) occur m the subequatorial belt and 
on mountain slopes ascended by the trade winds or the pre- 
vailing westerlies. Most of the dry and desert regions of 
the world (twenty inches of rain or less) are either low- 
lands of the trade-wind belt, like the Sahara and central 
Australia, or the slopes and lowlands to the leeward of 
lofty momitams, as in Peru, or continental interiors crossed 
by the westerly \vuids, as m central Asia. 

Exercise. Where are the regions of heaviest rainfall ? How are 
these regions related to the belts of the terrestrial winds ? to coast 
lines? to mountain ranges? Where are the regions of light rain- 
fall? How are these regions related to the terrestrial winds? 

The heaviest rainfall in the world occurs on the 
southern slopes of the Himalayas, north of the Bay of 



72 ELEMENTARY PHYSICAL GEOGRAPHY 

Bengal. Here the rainfall of a single year would meas- 
ure tliirty-five or forty feet in depth, and much more 
than half of this amount falls during the summer half 
year when the southerly monsoon is blowing. On the 
bold southwest coast of India an annual fall of over 
thirty feet occurs. 

The greater parts of western Europe and of eastern 
North America are fortunate in receiving a plentiful but 
not excessive ramfall. 

In the polar regions the annual snowfall, melted, would 
seldom exceed fifteen inches of water, and would fre- 
quently be less than ten. This is because cold air can- 
not contain much vapor, and because when cold air is 
cooled thete is but little vapor condensed from it. In 
the torrid zone the equatorial rains are heavier because 
warm air can contain a large quantity of vapor, and when 
warm air is cooled it yields an abundant condensation 
of moisture. 

51. Rainfall of the United States. — The ramfall of the 
United States may be considered' under three headings : 
the Pacific slope, the western interior region, the "eastern 
region. The Pacific slope has plentiful rainfall m the 
north (over sixty inches), where the storms of the west- 
erlies are common ; but it has light rainfall in the south 
(under thirty inches), because here the westerlies turn 
southward to join the trades, and storms are infrequent. 
The westerly winds are stronger and stormier in winter 
than in summer; hence the rainfall of Washington and 
Oregon is heavier in the winter than in the summer 



THE ATMOSPHERE 73 

months. The belt of westerly winds reaches farther 
south in winter than in summer ; hence the rainfall of 
southern California is almost entirely confined to the 
winter months, while the summers are very dry, thus 
illustrating the features of the subtropical belt. 



Fig. 29. Annual Rainfall of the United States 

Darkest shade, over 80 inches. Lighter vertical lines, from 40 inches to 80 inches. 
Horizontal lines, from 20 inches to 40 inches. Blank, from 10 inches to 20 
inches. Dotted, less than 10 inches. 



The western interior region, from the Cascade and Sierra 
Nevada mountains to the 100th meridian, has moderate or 
plentiful rainfall on the mountains and high plateaus, be- 
cause the air is cooled and some of its moisture is con- 
densed as the westerly winds rise over these elevations. 
The lower lands, as in the basins of Utah and Nevada 
and over the Great plains that slope eastward from the 



74 ELEMENTAEY PHYSICAL GEOGRAPHY 

Rocky mountains, have light rainfall. The winds here, 
already dried by losing much of their moisture m cross- 
ing the ranges farther west, are seldom cooled enough to 
form clouds and to yield rain. Hence much of this region 
is arid. A large part of Nevada, Utah, and Arizona is too 
dry to yield pasturage ; elsewhere a tliin growth of grass 
suffices to support cattle if they have a large area over 
which to range. Agriculture is seldom successful in 
this region without the aid of irrigation. 

The eastern region is not distinctly separated from 
the western; the rainfall gradually increases eastward, 
as moisture is supplied in greater quantities by south- 
erly winds from the Gulf of Mexico and from the 
Atlantic. Over most of -this great region rainfall is 
well distributed through the year (over forty or fifty 
inches) ; somewhat more falls in summer than in winter 
over the mid-Mississippi basin. The heaviest fall (over 
sixty or eighty inches) is on the states bordering the Gulf 
of Mexico (not including Texas), and on the mountains 
of North Carolina. 

52. Weather Changes. -^ The term weather includes all 
the atmospheric conditions that an observer may feel or 
see, — hot or cold, clear or cloudy, dry or wet, Avindy or 
calm. 

In the torrid zone the weather is marked by regular 
changes from day to night ; the changes are small at sea 
and greater on land, and they are seldom interrupted by 
storms, except that afternoon thunderstorms are common 
in the belt of equatorial rains. In the summer season of 



THE ATMOSPHERE 75 

temperate latitudes weather changes are usually of mod- 
erate amount. In winter the weather of temperate lati- 
tudes is largely controlled by the passage of cyclonic and 
anticyclonic areas, which are then numerous and large, 
while the control .by the change from day to night is rela- 
tively weak. 

In frigid latitudes the change of weather from day to 
night is always weak compared with the changes caused 
by the passage of the great atmospheric whirls. 

The relation of weather changes to the spiraling winds 
of the prevailing westerlies may be simply illustrated by 
drawing (on an appropriate scale) the winds and clouds 
of a cyclonic and an anticyclonic area, as in Figure 16, on 
tracing paper and moving the paper slowly to the right, 
across a map of the United States. Let the center of the 
cyclonic area be supposed to move, for example, in four 
days from Colorado past Lake Michigan and down Hie 
St. Lawrence river. Note the changes of wind and 
weather at Indianapolis, or some other place, as the spi- 
ralmg wind areas advance eastward. Consider the tem- 
perature of the regions whence the winds come in winter 
and summer, Figures 18 and 19, and infer the changes of 
weather that they will bring. In the diagram for winter 
weather the area of the spiraling winds should be larger 
than m summer ; the cloud sheet about the cyclonic center 
should be larger and the winds stronger. 

A series of cyclonic areas sometimes pass by at the rate 
of two in seven days, thus causing a repetition of a certain 
kind of weather on the same day of the week for several 
weeks together. 



76 ELEMENTARY PHYSICAL GEOGRAPHY 

53. Summer Weather in the United States. — A well- 
marked series of weather changes over the central and 
eastern United States in summer may open with fair 
weather and bright blue sky ; the days are warm but not 
oppressive ; the nights are cool and refi'eshing. Then, if 
a cyclonic center appears a thousand miles or so to the 
west, the wind changes to a southerly source, so that it 
comes from the warm waters of the Gulf of Mexico and 
the warmer land of the Southern States. The air becomes 
hazy and the sky pale blue ; the days are sultry and 
oppressive, and the nights lose their refreshing coolness; 
the ground is dried and parched, and vegetation suffers. 
The great corn crop of the Mississippi valley may profit 
by these high temperatures if they do not last too long, 
but manual labor is exhausting under the blazing sun, and 
sunstrokes occur in increasing numbers. 

Scattered thunderstorms are then reported for a day or 
two in the afternoon and evening. These are followed by a 
more extended cloudiness as the cyclonic center approaches, 
and general rains may fall over several states near the low- 
pressure center. Thunderstorms of great size are some- 
times formed in the moist southerly winds, occasionally 
giving rise to destructive tornadoes. As these local storms 
pass by, the cooler northwesterly winds in the rear of the 
low-pressure center come from the far northern plains. 
The clouds drift away eastward, the pressure slowly lises, 
the temperature falls 20° or more, and damp sultry air 
under heavy clouds is exchanged for fresh air with bright 
blue sky. Then, as the westerly winds weaken, a southerly 
breeze springs up and all these changes are repeated. 



THE ATMOSPHERE 77 

54. Winter Weather in the United States. — In winter the 
succession of weather changes is controlled even more dis- 
tinctly than in summer by the passage of cyclonic and anti- 
cyclonic areas. A period of fine, cold, anticyclonic weather 
usually has a cloudless sky with light winds. The weak sun- 
shine of a short midwinter day cannot overcome the strong 
cooling by radiation durmg the long clear night, and the tem- 
perature at dawn sinks to a low degree. But as the anticy- 
clone moves eastward the pressure begins to fall. Then long 
filaments of lofty cirrus cloud float slowly over from the west, 
announcing the approach of a cyclonic center, the wind turns 
to a more southerly source, and the temperature slowly rises. 

As the cyclonic center draws near, the wind strengthens, 
the sky is more heavily overcast, and the temperature rises 
more distinctly, for the source of the winds is now over 
the tempered waters of the sea on the south and southeast. 
The rise of temperature may continue steadily through the 
night, so that midnight and dawn are warmer than the pre- 
vious noon ; for the southerly wind may be more powerful 
as a cause of warming than the cloudy night is as a cause 
of cooling. The lowering clouds let fall their rain or snow ; 
if rain, the snow of former storms is rapidly washed away; 
if snow, the drifts of former storms are deepened and the 
country is shrouded in white far and wide. It is under 
the long-lasting snow cover that the "winter wheat" of 
the northern prairies, sown in November, is protected 
from the extreme cold of the winter winds, for the snow 
is an excellent non-conductor. 

As the cyclonic center moves on, the northwesterly winds 
follow it and the pressure rises. The rain or snow ceases ; 



78 ELEMENTARY PHYSICAL GEOGRAPHY 

the clouds break up and drift away to the east and reveal a 
brilliantly clear sky. The cold northwesterly gale that has 
come from the far northern plains, west of the cyclonic cen- 
ter, now arrives as a "cold wave." These winds may be 
from 30° to 50° colder than the southerly winds. A fall 
of temperature may thus be produced steadily through the 
day, so that noon is colder than the previous midnight. 

If the cold gale is accompanied by falling or drifting 
snow, it is called a blizzard, a dreaded storm on the plains 
and prairies. As the temperature falls, furnaces must be 
made hotter to keep houses warm, and destructive fires then 
become more frequent than usual. The cold winds may 
sweep far south, causing great damage to southern crops. 
Then, as the storm center moves eastward, the winds farther 
in its rear weaken; the nights become calm and the tem- 
perature falls to its lowest degree, and thus another spell 
of fine and intensely cold weather is ushered in. 

55. Summer and Winter Weather in Temperate Lati- 
tudes. — Both in winter and summer all the changes here 
described as connected with areas of liigh and of low 
pressure are felt earlier in the west than in the east. 
The eastward passage of cyclonic or low-pressure areas, 
illustrated in Figure 30, is controlled by the prevailing 
eastward atmospheric currents in' middle latitudes; and 
the direction of the currents is determined, as has been 
stated, by the earth's rotation. In summer time the 
difference of pressure between cyclonic and anticyclonic 
centers in North America is relatively small (from 0.5 to 
0.8 inch) ; hence the spiraling winds are tlien relatively 



THE ATMOSPHERE 



79 



light. Moreover, the southern and northern regions 
whence the inflowing spiral winds are then drawn have 
temperatures not greatly different (about 85° and 65°); 
hence the changes of temperature are moderate. The 
eastward movement of the cyclonic areas is relatively 




0° 30° 

Fig. 30. Stonn Tracks of the North Temijerate Zone 

slow (500 miles a day in the United States) ; hence the 
weather changes are gradual. 

All this is changed in winter. The differences of pres- 
sure are doubled (from 1.0 to 1.5 inches) and the winds 
often gain the strength of gales ; the regions whence the 
southerly and northerly winds are drawn upon the Cen- 
tral States have very unlike temperatures (80° and 0°), 



80 ELEMENTARY PHYSICAL GEOGRAPHY 

and the contrast between the warmth in the front and 
the cold in the rear of the cyclonic areas is very marked. 
In the winter hemisphere the general winds are quick- 
ened, especially in middle latitudes ; and therefore the 
centers of high and of low pressure drift eastward faster 
(800 miles a day). Besides all this, the cyclonic and 
anticy clonic centers are more numerous in winter than 
in Summer ; hence weather changes in winter are frequent 
as well as rapid and strong. Winter is therefore a time 
of stormy changes as well as of low temperatures, thus 
resembling the conditions of the frigid zone ; while sum- 
mer weather is comparatively even at a high temperature, 
like that of the torrid zone. 

56. Ocean Storms. — The stormy areas of the westerly 
winds drift from North America out upon the northern 
Atlantic ocean, as shown in Figure 30. Gales attend their 
passage, especially in the winter season, when a voyage 
across this ocean is much rougher than in summer. The 
gales caused by these stgrms are usually on the southern 
side of the low-pressure center, and hence from a western 
quarter. The general course of the storm centers is north- 
eastward, so that a cyclonic center that passes over New 
England or down the St. Lawrence valley is more likely 
to affect the weather of Norway than that of Spam. 
Storms from the North Pacific ocean come upon the west- 
ern coast of North America; they may before breaking up 
pass far inland or even cross the whole breadth of the con- 
tinent. The storms in the prevailing westerly wuids of 
the southern hemisphere encounter but little land m their 



THE ATMOSPHERE 81 

course. They are more severe in the southern wmter 
(June to August) than in the summer (December to Feb- 
ruary). South America reaches farther south than the 
other continents; hence vessels rounding Cape Horn must 
enter much farther into this stormy belt than in rounding 
the Cape of Good Hope, and the passage aromid Cape 
Horn is dreaded for this reason. 

57. Cyclonic Winds. — The inflowing spiral winds of 
cyclonic storms are often given special names in different 
parts of the world, according to the kind of weather they 
may bring. The cold wave of our wmters, sweepmg over 
the central and eastern United States from the far northern 
plams in the rear of cyclonic centers, has already been 
described. In western Europe the cold wind of winter is 
the northeaster, because the plains of northeastern Europe 
supply colder air than the ocean about Iceland. It occurs 
when a cyclohic center follows a more southerly track than 
usual. The blizzard of our plains corresponds to the 
buran of Siberia. No special name has been given m the 
United States to the sultry southerly wind that frequently 
brings unseasonably warm weather m front of a cyclonic 
center. It might be called a sirocco, after the Italian name 
of a similar wind. In the southern hemisphere cold winds 
come from the south, and hot winds from the north. In 
southern Australia the "wuid that corresponds to the sirocco 
is called a brickfielder, because it bakes the fields hard 
and dry. 

58. Weather Predictions. — Weather maps from which 
the general character of the weather for one or two days 



82 ELEMENTARY PHYSICAL GEOGRAPHY 



1 



may be predicted are now prepared daily in many countries 
Observations of the weather made at the same hour at 
many different places are telegraphed to the central station, 
— the Weather Bureau at Washington for the United 
States. They are then promptly charted so that the areas 
of high and low pressure, the temperature, the direction 
and strength of the winds, the distribution of clear and 
cloudy sky and of rain or snow are all shown. It is known, 
as described on preceding pages, that cyclonic and anti- 
cyclonic areas with their attending weather conditions usu- 
ally move eastward ; it is therefore possible to foretell with 
considerable accuracy the weather that may be expected 
for a day or two in various parts of the country from the 
conditions shown on the weather map. 

Predictions thus prepared are distributed by telegraph, 
and published in special bulletins and in newspapers for 
the benefit of the public. 

No one has yet succeeded in making successful predic- 
tions of the weather regularly for definite districts several 
weeks or months in advance. It is true that such "long- 
range predictions," as they are called, are frequently pub- 
lished. As the weather differs in different parts of the 
country, predictions of hot weather over the central United 
States in July and of cold weather in January, or rain in 
March and drought in September, may be correct for one 
place or another, but they must be incorrect for other 
places. Such predictions cannot be depended upon. 

59. Climate. — The general succession of weather 
changes through the year, averaged for many years, 



THE ATMOSPHERE 83 

constitutes the climate of a region. The five climatic 
zones into which the earth is commonly divided need 
further subdivision in order to correspond to the many 
well-marked types of climate on lands and seas, on coasts 
and inland regions, on lowlands and highlands. 

The trade-wind belt at sea has the simplest climate in 
the world, with small daily and yearly changes of tempera- 
ture. The steady wind and fair weather of almost any 
day give a fair sample of the year. Low lands under 
the regular trade winds suffer greater daily and yearly 
changes of temperature, with light rainfall. 

Compare the mean annual range of temperature in the "^^sf 
Indies and in inner Africa, latitude 20° N., Figure 20 ; in^A^frica, 
Indian ocean, and Australia, latitude 20° S. ^^-"^ 

The subequatorial belt has^a distinct seasonal change 
as the clouds of the heatequator move away and give 
place to the dry tj:ara.e winds. The Sudan, between the 
desert of Sahara and the forest belt of equatorial Africa, 
has plentiful rainfall and active plant growth when the 
equatorial cloud belt moves north, bringing the wet sea- 
son (May to August), but it becomes parched, barren, and 
dusty under the trade winds of the dry season (December 
to March), 

Examine Figure 21 and state in what months you would expect 
rain on or near the geographical equator. At the head of the Gulf 
of Guinea, west equatorial Africa, I'ain is most abundant in March 
and October to November. In Ceylon the rainfall is greater in May 
and October than in the other months; at the city of Quito, Ecua- 
dor, in April and November. How do you explain these double 
rainy seasons? 



84 ELEMENTARY PHYSICAL GEOGRAPHY 

The south temperate zone is mostly an oceanic belt. 
The changes of air temperature with the seasons are small, 
as shown in Figure 20, because the water surface warms 
and cools so little in summer and winter. Its winds are 
more stormy in winter, less stormy in summer ; never 
very hot or extremely cold, but for the most part chill, 
damp, and blustering. Islands near 50° S. are hardly 
habitable, not that the winters are too severe, although 
cloudy and wet, but that the summers are too chilling. 

The north temperate zone contains large areas of both 
land and water, and the temperatures of its various parts 
are therefore very unlike, as shown in Figures 18, 19, and 
20. The parallel of 50° N. crosses regions whose climates 
are so different that they Avould hardly have been placed 
under a single zone had they been studied before being 
named ; but the name was given from the truly temper- 
ate climate of southern Europe, before other parts of the 
world were well known. 

Beginning in the moderate climate of the North Atlantic, 
Figure 20, the parallel of 50° N. enters the favorable 
climate of middle Europe, where the last thousand years 
have witnessed the greatest human progress in the arts 
and sciences that the world has ever known. It crosses 
the broad deserts of central Asia, where the scattered 
population is held down in barbarism chiefly by severe 
and unfavorable climatic conditions. 

The broad North Pacific has in this latitude a climate 
as moderate as that of the North Atlantic. Passing the 
tempered and moist climate of the coast belt of British 
Columbia, and crossing the snowy mountain ranges beyond. 



THE ATMOSPHERE 



85 



the severe interior climate of middle Canada is reached, 
with extremes of temperature, summer and winter, only 
less than those of inner Asia. As far as habitability is 
concerned, the middle north temperate zone contains 
climatic differences almost as great as those found in 
passing from the equator to the pole/ 

Compare this account of the climate of latitude 50° X. with the 
conditions in latitude 50° S. 



Supplement to Chaptek II 

60. Deflection of Winds by the Earth's Rotation. — Place a marble 
in the center of a circular board. Set the marble in motion by 
striking it a light blow. It will move 
in a straight line along a radius from 
center to circumference. Now let the 
board be given a slow movement of 
rotation around a pivot at its center. 
The marble will now again move 
directly outward, but the line that it 
traces on the turning board will be 
curved so as to fall behind the radius 
on which it started. If the board 
turns to the left, the marble will be 
deflected to the right of its original 
path ; if the board turns rapidly, the 
deflection will be strong. 

In Figure 31 the circle. A, resting 
on the earth in a northern latitude ^ig. 31. Rotation ot a Disk on a 
may be taken to represent a circular Rotating Globe 

board or surface of great size. A 

north line drawn from the center of the circle meets the prolonged 
axis of the earth at N. "When the rotation of the earth has car- 
ried the cii-cle to B the same north line has a new direction, BN, 




86 ELEMENTARY PHYSICAL GEOGRAPHY 

showing that the circle has turned somewhat to the left with respect 
to its own center. Hence any such circle may be taken to represent 
a turning surface. A body beginning to move in any direction from 
the point A will tend to turn to the right, because of the rotation of 
the circle to the left. This tendency will be strongest at the pole, 
because a circle there rotates with the greatest rapidity, turning 
completely round in twenty-four hours. The tendency is zero at the 
equator, because there a circle has no movement of rotation with 
respect to its own center. In the southern hemisphere, where the 
circle must turn to the right, the deflective force acts to the left. 

The wind is so free to move over the earth's surface that it is 
greatly affected by the deflective force arising from the earth's rota- 
tion. Hence the members of the atmospheric circulation do not flow 
north and south, but are always deflected to the right of these direc- 
tions in the northern hemisphei'e, and to the left in the southern. 

The lofty overflow currents are deflected so as to run from the 
southwest or even from the west-southwest in the northern hemi- 
sphere, from the northwest or west-northwest in the southern. The 
winds approaching the equator do not blow directly from the north 
and the south in the two hemispheres, but are deflected so as to blow 
from the northeast and southeast, forming the trade winds. The 
whirling winds of cyclonic storms, described on pages 45 and 67, 
attempt to blow toward their centers of low pressure, but on account 
of the earth's rotation the winds are deflected to the right in the 
northern hemisphere, and to the left in the southern ; thus the storms 
are given their whirling movement. 

It should be noted that winds wiU be deflected to the right or left, 
in whatever direction they begin to blow, east and west winds being- 
affected just as much as north and south winds. Ocean currents are 
similarly affected but to a less degree, because they move moi'e 
slowly than the winds. Rivers tend to tui-u to the right in the 
northern hemisphere and to the left in the southern; but the 
tendency is practically overcome by the resistance of the banks. 
Similarly a railroad train tends to be deflected, but is held to its 
track by the flanges on the wheels. 



THE ATMOSPHERE 8T 

61. Practical Method of studying Observations of the Sun. — In 

studying the control of the seasons by the sun it is desirable to 
determine the length of the day and the midday altitude of the sun 
by observations about once a fortnight, or at least once a month, 
through the school year, with additional observations near the times 
of shortest and longest days or of lowest and highest midday sun. 

If sunrise comes at too early an hour for convenient observation, 
note that midday occurs at the middle of the interval between sun- 
rise and sunset. Midday is determined by the method explained on 
page 8. The time of sunset may be directly observed. The time 
of sunrise may then be determined by counting back as many hours 
and minutes before midday as sunset occurs after midday. 

The midday altitude of the sun may be determined as follows : 
Use such a box as is shown in Figure 3, and drive a pin square into 
one side of the box, close to its upper corner. With the pin as a cen- 
ter, draw an arc of a circle on the box side. Draw a horizontal and 
a vertical line from the pin to the arc. The arc included between the 
two lines will be a right angle, or 90°. Divide it into halves, divide 
the halves into thirds, and the thirds again into thirds. The small 
divisions thus found will be 5° of arc. Number the divisions from 
at the horizontal line to 90° at the vertical. 

As the sun approaches the meridian, turn the side of the box so 
that it is directed toward the sun. The shadow of the pin is then 
seen as a slanting line, and the altitude of the sun is indicated by 
the angle that the shadow line makes with the horizontal line. Con- 
tinue to turn the box after the sun, until the altitude indicated by 
the shadow line begins to decrease. The greatest angle thus found 
is the midday altitude of the sun. 

In Figure 32 let the horizontal scale represent the days of the 
year, and the vertical scale the angular altitude oi" the sun at mid- 
day. IMark the sun's midday altitude by dots opposite the appro- 
priate dates. At the close of the school year draw a curve through 
the dots. Draw lines parallel to the base line and touching the 
upper and lower points of the curves. Draw a third line midway 
between the last two. 



88 ELEMENTARY PHYSICAL GEOGRAPHY 

In Figure 33 the vertical scale represents the days of the year ; 
the horizontal scale measures hours before and after midday. Mark 
dots to the right and left of the midday line and opposite to the 
appropriate dates, to represent the time before and after midday at 
■which sunrise and sunset occur. Connect these dots by curved lines. 
Draw two lines that shall stand six hours on either side of the mid- 
day line. 

Now determine from Figure 32 the dates when the sun has the 
greatest midday altitude (or when it stands farthest north in the sky) 
when it has the least midday altitude (farthest south in the sky), 



yept. , Oct. , Nov, I Dec. , Jan. , Feb. , Mar, , Apr, ^ May , June , 
Fig. 32. Diagram of the Sun's Midday Altitude 

and the two dates when its altitude is that of the mid-horizontal 
line. Deterjuine from Figure 33 the date when the day is longest, 
when it is shortest, and the two dates when it is twelve hours long. 
Compare the dates thus found. If the observations are well made 
and the diagrams accurately constructed, the four dates should agree 
on the two diagrams. 

The dates when the days are twelve hours long, and therefore 
equal to the nights, are JNIarch 21 and September 22 ; these dates 
are called the vernal (spring) and autumnal (fall) equinox (equal- 
night). The date when the sun is farthest north, and when the day 
in the northern hemisphere is consequently longest, is June 2L 
This is called the summer solstice (sun-stand), because the sun, hav- 
ing then finished its northward movement, stops or "stands" before 
beginning its southward movement. Tlie day when the sun is 



THE ATMOSPHERE 



89 



farthest south, and when the day is consequently shortest in the 
northern hemisphere, is called the winter solstice; this date is 
December 21. 

Between what dates is the sun moving northward in the sky? 
Between what dates is it moving southward ? Between what dates 
are the days lengthening? 



12 



M 



Se|)t 



At the time of the equi- 
noxes the sun must be on 
the equatoi- of the sky ; for, 
as is shown in Figure 17, 
it is only then that equal 
days and nights occm* in all 
parts of the world. Hence 
the middle horizontal line 
in Figure 32 must rejire- 
sent the angular altitude 
of the sky equator where it 
ci'osses the meridian. The 
angular distance of the sun 
north or south of the sky 
equator for any day of the 
year may be measured by 
the scale at the side of 
the figvu-e. The greatest 
angular distance of the sun 
from the sky eqiiator gives 
means of determining the 
limits of the zones. (See 
page 48.) 

How far north of the sky equator does the sun stand at the time of 
the summer solstice ? How far south at the time of the winter solstice ? 
How many days is it north of the sky equator? How many days south ? 

62. Determination of Latitude. — The sky equator passes overhead 
(in the zenith) to an observer at the earth's equator ; hence the sky 
equator will depart one degree from the zenith for every degree that 



Apr. 



M^y 



Jily 



Fig. 33. 



Diagram of Sunrise and 
Sunset Hours 



90 ELEMENTARY PHYSICAL GEOGRAPHY 

the observer moves toward the pole. Therefore the latitude of a 
place must equal the angular distance of the sky equator from the 
zenith. Latitude may thus be determined on any day by measuring 
the sun's midday altitude and allowing for its distance from the sky 
equator, as determined by Figure 32. The altitude of the sky equa- 
tor subtracted from 90° is the latitude. Results that are correct 
within a few degrees may be obtained even by the rough obser- 
vations here described. 

If records of the kind indicated above are taken on different dates 
in successive years, the increasing number of dots will give better and 
better definition of the curves in Figures 32 and 33 ; but minute 
accuracy of performance is not so important as intelligent exercise in 
the application of principles. 

Examples. If the midday altitude of the sun is 50° on the 22d of 
September, what is the latitude of the place of observation ? What 
would the latitude be if the observation had been made on Decem- 
ber 21 ? on March 21 ? on June 21 ? 

63. Exercises on Weather Maps. — Many instructive exercises 
may be based on the daily weather maps. Copies of these maps for 
school use may be obtained, under certain conditions, by addressing 
the Chief of the Weather Bureau, Washington, D.C. The exercises 
here described may be performed on the original maps, or on outline 
maps of the United States upon which certain weather elements are 
copied. It is usually best to select maps on which differences of 
pressure are well defined, in order to exhibit strongly marked types 
of weather. 

64. Distribution of Pressure. — Plat upon a blank map of the 
United States the barometer readings taken from a weather map, 
and thus guided draw in lines of equal pressure, or isobars, for every 
tenth of an inch according to the method already explained for iso- 
therms. The difference of pressure between the highest and lowest 
readings is.often six or eight tenths of an inch or more. Shade the 
areas of high and low pressure, leaving the area of intermediate pres- 
sure (for example, from 29.9 to 30.1 inches) blank. Describe the 



THE ATMOSPHERE 91 

distribution of pressure thus shown. Draw a similar map for the 
next day. Describe the change in the distribution of pressure thus 
found. Temperature may be similarly treated. 

65. Movement of Winds in Areas of High and Low Pressure. — 

Select several well-defined examples of high- and low-pressure areas 
whote centers lie in the mid-Ohio valley, so that observations are 
provided on all sides of them. Plat the wind arrows (the arrow 
flies with the wind on weather maps), and let their length indicate 
wind velocity (an eighth of an inch for five or ten miles) . Draw addi- 
tional lines to represent inferred wind movement between the points 
of observation. How is the direction of the wind at any place 
related to the distribution of pressure about that place ? In answer- 
ing this question it will be well to draw, through the point consid- 
ered, a line at right angles to the neighboring isobars. This line 
shows the direction of increase or decrease of pressure. Describe 
the general movement of the winds (direction and velocity) with 
respect to a center of high pressure ; of low pressure. 

66. Composite Portrait of High- and Low-Pressure Areas. — Rule 

a straight line through the center of a sheet of tracing paper and mark 
the ends of the line N and S. Lay the center of the sheet over the 
center of an area of low pressure and turn the N-S line so that it 
shall lie most nearly parallel to the adjacent meridians. Trace off 
the signs indicating the state of the sky (clear, fair, rain, or snow) at 
various stations. Do the same for several other maps that have a 
low-pressure center. Do the same on another tracing paper for sev- 
eral areas of high pressure. Compare the results as to the distribu- 
tion and frequency of clear, fair, and wet weather, with respect to 
centers of high and of low pressure. Winds may be similarly 
treated. 

67. Progression of High- and Low-Pressure Areas. — Select a series 
of four or five maps on which a well-defined area of high or 
of low pressure is represented as occupying successive positions 
eastward across the country from the Rocky mountains to the 
Atlantic. Chart on an outline map the path of the center of the 



92 ELEMENTARY PHYSICAL GEOGRAPHY 

area studied and determine its velocity in miles an hour and a day. 
Note the weather changes (pressure, temperature, wind, sky) that 
occur at a single station as the cyclonic or anticyclonic area passes 
over it. What is the general character of these changes for a cyclonic 
area ? for an anticyclonic area ? 

Compare the succession of weather changes at any place, as deter- 
mined from weather maps, with the weather changes observed at 
school during several days. How are the local weather changes 
related to passing areas of high or of low pressure (anticyclonic and 
cyclonic areas) ? 

QUESTIONS 

Sec. 19. What processes depend on the atmosphere? What is 
known of its height? 

20. What is the composition of air? How is oxygen iisec: ? 
carbonic dioxide ? 

21. What is the pressure of the atmosj^here on a square foot of 
surface ? Describe the mercurial barometer ; the aneroid barometer. 
How can barometers be used to measure mountain heights ? 

22. How does the density of the air vary? Why? What is the 
weight of a cubic foot of air at sea level ? How is sound carried ? 

23. How are the colors of the sky produced? What is the twi- 
light arch? When may it be seen? 

24. How is the temperature of the air controlled? Why is the 
upper air cold? Consider the diurnal range of temperature in the 
upper and lower air. How do the processes of absorption, conduc- 
tion, and radiation affect the temperature of the air ? How does the 
form of the earth affect the distribution of temperature ? How is 
the weight of air affected by heat ? 

25. What is a mirage? How is it produced on level deserts? 
on a water surface ? 

26. Explain the construction of a thermometer. How do the 
Fahrenheit and Centigrade thermometer scales differ? What is a 



THE ATMOSPHERE 93 

thermograph? a maximum thermometer? a minimum thermom- 
eter? How should a thermometer be exposed? 

27. How are temperature charts constructed? What is an iso- 
thermal line? How are mean temperatures determined? What 
is the heat equator ? Describe its position. Compare the mean 
annual isotherms of the northern and southern hemispheres. 

28. Describe the movements of the air between a hot and a cold 
room. What is a convectional circulation? Describe the general 
circulation of the atmosphere between equator and poles. What 
changes of temperature are caused in ascending and descending 
currents ? What is the planetary circulation ? 

29. How are winds named? How is their strength described? 
What is an anemometer? 

30. Describe the steps in the circulation of water through the 
atmosphere. How is rain caused? 

31. What are the chief members of the planetary winds? 
Describe the trade winds. Where do they occur? AVhat is their 
direction? What is the relation of rainfall and deserts to the 
trade winds? of wet and dry mountain slopes to the trade winds? 
Give examples. Describe the prevailing westerlies. Where do they 
occur? What is their direction? How is rainfall related to these 
winds? What are the doldrums? the horse latitudes? Describe 
and explain the weather of the doldrums ; of the horse latitudes. 

32. Describe the whirls of the westerly winds. Explain their 
weather. How fast do they travel ? Compare the whirls of the 
two hemispheres. Compare the atmospheric pressure at the center 
of the inward and outward whirls. What names are given to these 
whirls ? 

33. Describe the movement of the earth around the sun. Com- 
pare the attitudes of the northern and southern hemispheres with 
respect to the sun in the two half years. What are the resulting 
variations of temperature ? What are the months of each of the four 
seasons in the northern hemisphere? in the southern? What are the 
limits of the torrid zone ? the frigid zones ? the temperate zones ? 



94 ELEMENTARY PHYSICAL GEOGRAPHY 

34. What are the apparent movements of the sun in December? 
in June ? How are the temperatures of winter and summer related 
to these movements? Explain the rising temperature of spring; 
the falling temperature of autumn. 

35, 36. How may the change of seasons be described if the earth 
as a whole is considered ? Mention the most striking facts shown on 
the isothermal charts for January and for July. 

37. Describe the most striking facts shown on the chart of mean 
annual temperature range. Compare the annual range of temperature 
over the northern continents and the southern oceans ; on western and 
eastern coasts in temperate latitudes. Why are the annual changes 
large in the northern hemisphere? Why small in the southern? 

38. How do the terrestrial winds differ from the planetary? 
Explain the differences. Describe and explain the subtropical 
belts. Name some countries lying in a subtropical belt and describe 
them as to winds and rainfall. Describe and explain the subequar 
torial belt. Describe its migration, Figures 22, 23, on the Atlantic 
ocean; on the eastern Pacific ; on the Indian ocean. Give some 
examples of subequatorial rainf aU in South America ; in Africa. 

39. What are monsoons? How are they caused ? Where do they 
occur, Figures 22, 23 ? Describe the monsoons of the Indian ocean. 

40. 41, 42. How do the continents affect the terrestrial winds? 
Give examples from Asia. What are land and sea breezes? How 
do fair-weather winds on lands vary from night to day? Explain 
this variation. Why does it not occur at sea ? 

43. What is humidity? How does it vary with temperature? 
What is saturation? Compare the feeling of damp and dry air. 

44. What is the dew-point ? How may it be determined ? What 
are dew and frost ? Under what conditions are they produced ? 

45. Describe the chief kinds of clouds : cumulus, cirrus, cirro- 
stratus, alto-nimbus, and nimbus. Describe a halo ; a corona. 

46. 47, 48. Describe a thunderstoripi. Where and when do such 
storms occur? What can you say about lightning and thunder? 
What is a cloud-burst? a rainbow? a tornado? a waterspout? 



i 



THE ATMOSPHERE 95 

49. Where and how are tropical cyclones formed? How do their 
winds blow ? How do these storms travel ? In what regions do they 
occur? In what months? Why are there two seasons of cyclones 
in the northern Indian ocean? Why are tropical cyclones not 
formed in the South Atlantic ? 

50. What is meant by rainfall? Describe and explain snow ; rain ; 
liail ; frozen rain. How is rainfall measured ? State the relation of 
rainfall to agriculture. Give several examples of the relation between 
the terrestrial winds, Figures 22, 23, and rainfall. Figure 28. Where 
is the heaviest rainfall of the world ? What is its amount? its cause ? 
Why is the rainfall of low latitudes large, and of high latitudes small ? 

51 . Describe the rainfall of the Pacific slope of the United States ; 
of the interior region ; of the eastern region. 

52. What is meant by weather ? Describe the prevailing weather of 
the torrid zone ; of the temperate zones in summer ; in winter ; of 
frigid latitudes. Explain the effects of cyclonic and anticyclonic areas. 

53. Describe a period of summer weather in the eastern United 
States as a cyclonic area is approaching ; after it has passed. When 
are sunstrokes and thunderstorms most common? 

54. Describe our winter weather in front of a cyclonic area ; in 
the rear. When may a warming night occur? a cooling day? 
What is a cold wave ? a blizzard ? 

55. Describe the tracks of high- and low-pressure areas in the 
north temperate zone. What changes of pressure do they cause 
in summer? in winter? How fast do they travel in summer? in 
winter? Compare the changes of temperature that they produce 
in the central part of United States in summer and in winter. 

56. 57, 58. Describe the storms of the North Atlantic. What is 
aburan? a sirocco? a brickfielder ? How is the weather predicted? 

59. W^hat is climate? Describe the climate of the trade-wind 
belt at sea ; of the subequatorial belt ; of the south temperate zone ; 
of the north temperate zone on the oceans ; on the lands. Describe 
the climates of latitude 50° N. ; of latitude 50° S. 



I 



CHAPTER III 
THE OCEAN 

68. Form of the Ocean. — The ocean is a sheet of salt 
water, clear and blue, covering about three quarters of the 
earth's surface to an average depth of about two miles. 
It lies in broad depressions or basins between tlie conti- 
nents, its shallow edges lapping over the margin of the 
continental masses. 

The outline and distribution of the ocean are best 
studied on a globe. A vast water area, comprising the 
Pacific and Antarctic oceans, covers nearly half the earth. 
The water surface is broken only by Australia, the Antarc- 
tic lands, and many small islands. A short Indian arm 
extends from this great oceanic area into the space between 
Africa and Australia, and a long, relatively narrow Atlan- 
tic arm runs between the Old and New Worlds, ending in 
the gulf-like Arctic ocean around the north pole. 

The surface of a hemisphere whose pole is near New 
Zealand is nearly all water, as in Figure 34 ; while the 
opposite hemisphere contains all the large land areas, 
except Australia, the Antarctic lands, and the extremity 
of South America. It is not a little curious to note that 
near the pole of the land hemisphere stands the greatest 
city of the world, the capital of the empire whose colonies 
are more widely spread than those of any other nation. 

96 



THE OCEAN 



97 



What lands lie entirely in the land hemisphere? What oceans 
lie largely in the land hemisphere? Trace the course of the great 
circle which divides the land and water hemispheres. 

69. The Ocean as a Highway. ^ — The lands are widely 
separated by the oceans, and navigation of the "high seas" 
requires great skill and is fraught with many dangers. 
But the oceans are a ready-made highway, where movement 




Fig. .34. Water and Land Hemispheres 

is easy and open to all comers ; the winds furnish free motive 
power to sailing vessels, and coal is an economical fuel for 
steamers. Hence ocean-going vessels are used to carry 
large quantities of merchandise from one part of the world 
to another. 

Before railroads were invented the two sides of the North 
Atlantic were in more active communication by sea than the 
two sides of any continent overland. Since railroads have 
been extensively built inland transportation has greatly in- 
creased ; but a great part of international commerce is still 
carried on across the oceans in steamships and sailing vessels. 



98 



ELEMENTARY PHYSICAL GEOGRAPHY 



70. Exploration of the Ocean. — The earlier exploration 
of the ocean discovered its shore lines on the continents and" 
islands. Exploration in the latter part of the nineteenth 
century penetrated its depths and reached its bottom. 

Soundings are now made with much accuracy, even to 
depths of four miles or more. I'ine steel wire is used for 




Fig. 35. An Ot'eaii Steamship 

a line ; the sinker is a heavy iron ball that is automatically 
detached on touching the bottom; then the wire is rapidly 
reeled in by steam power. A sounding of 3000 fathoms 
• {one fathom equals six feet), or over three miles, can be 
completed in about an hour. 

The temperature of the deep water is taken by self- 
registering thermometers. They must be protected by an 
outer glass tube against the tremendous pressure of the 



THE OCEAN 



99 



deep water. Samples of water are obtained from various 
depths by the use of brass tubes, called water bottles, sent 
down open but automatically closed when 
reeling in begins. Specimens of the ocean 
bottom are gathered by dredges, or strong 
nets with an iron rim. Wire rope is needed 
to haul up the ton or more of material 
that they take in while dragging on the 
sea jfloor at depths of one, two, or even 
tliree miles. Nets are sometimes attached 
to the wire rope at different depths, for 
the purpose of catching animals that hap- 
pen to enter them. The best nets are 
closed while sinking 
and rising, being open 
only while trolling at 
the greatest depth 
that they reach. 




Fig. 36 

Sounding Instrument 

and Water Bottle 



71. Ocean Depths. — Soundings have 
shown that the ocean basins are com- 
paratively steeps sided and flat floored. 
The greatest depth yet found is 31,614 
feet, in the western Pacific near the 
island of Guam (lat. 12° 45' N., long. 
145° 45' E.). Another place of great 
depth, 30,930 feet, is in the Pacific, 
near the Fiji islands. 

The deepest sounding yet made in the Atlantic is 27,366 
feet, or over five miles, in a local depression 100 miles north 




Fig. 37. Dredare 



L.oFC. 



100 ELEMENTARY PHYSICAL GEOGRAPHY 

of Porto R.ico, West Indies. The Atlantic is generally less 
deep along its middle (9000 to 12,000 feet) than on either 
side (15,000 to 18,000 feet), the shallower middle part 
being sometimes called a ridge or swell. (See Figure 144.) 

72. Composition and Density. — The ocean contains a 
great variety of substances in solution, for it has received 
everything that streams have dissolved and carried from 
the lands for ages past. Common salt makes three quarters 
of the dissolved substances. An important but much less 
plentiful dissolved substance is limestone, of which many 
sea animals make their shells or skeletons. 

A small quantity of atmospheric gases is foimd dis- 
solved in sea water, even in its deepest parts. The gases 
are taken in at the surface, especially when air is caught 
in dashing waves. It is upon the oxygen thus supplied 
that fish and most other marine animals depend for breath- 
ing; but whales and other mammals living in the ocean 
come to the surface for air. 

The mineral substances dissolved in ocean water make 
about three per cent of its weight ; their presence makes it 
a little heavier than pure water (in proportion of 1.026 to 
1.000). Although water is easily moved, it can be very- 
little compressed. Hence, in spite of the great pressure of 
the upper layers of the ocean on those beneath, the ocean 
is unlike the atmosphere in being of nearly uniform density 
from top to bottom. Anything that is heavy enough to 
sink at the top will sink all the way to the bottom. 

73. Color and Phosphorescence. — In the open ocean, far 
from land, the water is extraordinarily clear. It is of a 



THE OCEAN 101 

beautiful deep blue, so strong that one would expect the 
color to show in a bucket ; but if some water is dij)ped up 
from the sea surface, it appears perfectly transparent and 
colorless. In cloudy weather the ocean is of a duller, 
more leaden hue. Near the lands the blue is lighter and 
turns toward a greenish shade. Opposite large rivers the 
water may be yellowish from suspended sediment; the 
Yellow sea is so named on this account. What large 
rivers enter it? 

There are many small jellylike animals that float in the 
ocean. Some of these have the power of emitting, when 
disturbed, a pale light, visible in the dark. They are 
found chiefly in the warmer parts of the ocean. Break- 
ing waves and the foam in the wake of a vessel may thus 
become beautifully luminous or phosphorescent at night. 

74. Ocean Temperatures. — The surface layers of the 
ocean vary in temperature with latitude, reaching about 
80° around the equator, and being reduced to 30° or 28° 
in the polar regions (Figure 44). The great body of the 
deep ocean is cold in all latitudes ; its temperature is about 
30° in high latitudes and 35° or 40° in the torrid zone. 

When exploring vessels dredge in a torrid ocean the 
sediments brought up from the bottom have a tempera- 
ture near freezing, strangely in contrast with that of the 
objects on shipboard under a hot sun. 

The sun's rays have small effect on ocean water at 
depths below 100 or 150 fathoms. At greater depths the 
ocean must be nearly dark, with hardly perceptible dif- 
ference between day and night, or between winter and 



102 ELEMENTARY PHYSICAL GEOGRAPHY 

summer. The temperature at any point in the great body 
of the deep ocean is therefore nearly constant. 

Changes of temperature in the ocean surface through 
the day or the year are very small, seldom more than 3° 
and 15°, respectively. As the temperature of the lower 
air is largely controlled by that of the surface on which 
it rests, the climate of islands in mid ocean and of conti- 
nental borders where the prevailing winds blow ashore is 
free from great changes of temperature between winter 
and summer. 

Salt water becomes heavier and heavier as it is cooled 
down to its freezing point, 28°. Hence the cold surface 
water of high latitudes sinks to great depths and creeps 
very slowly toward the equator; thus the low tempera- 
ture of the great body of the ocean is accounted for. 

Fresh water is unlike salt water in being densest at 39". 
On being warmed or cooled from this temperature it expands 
and becomes lighter. Hence in winter, when all the water 
of a lake has been cooled to 39°, further cooling affects only 
the surface water, which may then soon freeze. 

75. Ice in the Ocean. — Ice expands a little as it freezes ; 
it therefore floats, about one seventh of its volume being 
out of water. The ice formed in the polar oceans is 
known as floe ice ; it may reach a thickness of from three 
to seven feet in a single winter. 

Great fields of floe ice drift with the winds and currents. 
They may thus be torn apart or crushed together. When 
two floes collide pack ice of very irregular surface is 
formed; it may reach a thickness of over 100 feet. 



THE OCEAN 



103 



In Greely's expedition to the Arctic regions in 1883 
his boats were frequently in danger of being crushed 
when ice fields drifted together, closing the water passage 
he had been following. 

Smooth floe ice is easily crossed on sleds. The Eskimos 
make winter journeys upon it. Where packed it may be 




Fig. 38. A Vessel beset by Pack Ice 

impassable. It was on account of the roughness of ridged 
pack ice that Nansen had to turn back from his " dash for 
the pole," in latitude 86° 13' N., longitude 96° E., on 
April 8, 1895. When two large fields of pack ice drift 
together a vessel between them would be crushed, unless 
of great strength and shaped so as to escape by rising. 
Nansen's vessel, the " Fram," was especially constructed 
to withstand great pressure and so survived the dangers 
to which it was exposed. 



104 



ELEMENTARY PHYSICAL GEOGRAPHY 



Icebergs in the North Atlantic are fragments from the 
ends of great fields of ice (glaciers) that descend into the 
sea from Arctic lands, chiefly Greenland ; they are of 
fresh water. The tabular icebergs of the Antarctic ocean 
are fragments of a heavy sheet of ice around the south 
pole. Some of these ice blocks measure a mile or more 




Fig. 39. An Iceberg 

on a side, and 1200 to 1500 feet in thickness. Icebergs, 
being of fresh water, float with about one sixth or one 
seventh of their volume above the sea surface. 

Collision with an iceberg is one of the dreaded dangers 
of navigation in high latitudes. In the southern oceans 
drifting icebergs reach latitude 50°, or even 40°. In the 
North Atlantic they reach latitude 45°, southeast of New- 
foundland, but they are absent from the northwestern 
coast of Europe, even in latitude 70°, on account of the 



THE OCEAN 



105 



warm water there prevailing. They are wanting in the 
North Pacific, except in the seas of northeastern Asia. 

76. The Ocean Bottom. — The greater part of the deep 
ocean bottom is a comparatively even plain of soft ooze. 
The plain rises and falls gently in broad swells, but is not 



Fig. 40. Globigerina (magnified 100 times) 

varied by hills and valleys such as occur on the lands. 
A large part of the deep sea bottom is covered with a fine 
deposit, called ooze, which consists of the minute shells, 
more or less decayed, of s.imple animal forms that live at 
or near the surface. One of these, highly magnified, is 
shown in Figure 40. In the deepest oceans the bottom 
is covered with a fine reddish clay. Nearer the shores 



^ 




106 ELEMENTARY PHYSICAL GEOGRAPHY 

the deposits become muddy with sediments derived from 
the land. It is by the very slow but long-continued accu- 
mulation of these deposits that the ocean floor has been 
made so smooth. 

" The monotony, dreariness, and desolation of the deeper 
parts of this submarine scenery can scarcely be realized. 
The most barren terrestrial districts must seem diversified 
when compared with the vast expanse of ooze which covers 
the deeper parts of the ocean." 

No mountain ranges with sharp peaks and ridges 
separated by deep passes and valleys have yet been dis- 
covered on the open ocean floor far from the conti'- 
nents ; but Cuba and some of the neighboring islands 
in the West Indies seem to be the crests of a mountain 
range whose western extension forms submarine ridges 
in the northern Caribbean, connecting the islands with 
Central America. 

Volcanic and coral islands rise with steep slopes from 
the deep ocean. Volcanic cones sometimes rise above the 
ocean surface, forming lofty mountains, as in the Hawaiian 
islands ; sometimes they are known only by soundings, 
their summits being below sea level. 

77. Mediterraneans. — Besides the open oceans thus far 
considered there are several deep seas, more or less separated 
from the oceans by land barriers. The most important of 
these is the classic Mediterranean (the sea ■•' m the middle 
of the lands ") ; its average depth is nearly as great as that 
of the great oceans, but it is connected with the Atlantic 
only by the narrow and shallow Strait of Gibraltar. 



THE OCEAN 107 

Other similar mediterranean seas are the Caribbean and 
the Mexican (deep central part of the Gulf of Mexico), 
adjoining the western Atlantic ; and the Japan, China, 
Sulu, and some smaller seas imperfectly inclosed from 
the western Pacific by island chains. The deep water 
of mediterraneans is warmer than that of the neighbor- 
ing oceans, whose cold bottom waters cannot enter the 
mclosed basins. 

78. Continental Shelves The ocean often overlaps 

the borders of the continental masses in a comparatively 
shallow belt of water, at whose outer edge the depth is 
commonly about 600 feet; thence it rapidly sinks to the 
deep ocean floor. These shallow bottoms are known as 
continental shelves. The water on the shelf is often 
greenish from fine suspended sediment, unlike the clear 
deep blue water of the open ocean. 

A well-defined continental* shelf, from 50 to 100 or 
more miles in width, stretches along the eastern side of 
North America from Newfoundland to Florida, and thence 
around the Gulf of Mexico. The British Isles stand upon 
a continental shelf that borders mid-western Europe. The 
Malayan and Australasian islands surmount broad shelves 
between Asia and Australia, separated by a belt of deeper 
water. 

The gravel, sand, and clay washed from the lands into 
the seas are moved about by waves, currents, and tides 
on the continental shelves. Thus the land waste is slowly 
ground finer and finer, and its finest particles are gradu- 
ally moved outward to (peeper water. They are seldom 



108 ELEMENTARY PHYSICAL GEOGRAPHY 

found ill dreclgings over 200 miles from shore; for the 
most part they are carried a less distance. 

In the course of years, centuries, and ages the sedi- 
ments thus accumulating on a continental shelf may 
form successive layers, each a few inches or feet in 
thickness, accordmg to the rate of supply. A layer of 
sediments of this kind is called a bed or stratum (plural, 
strata). Many strata laid down on the sea floor, one 

Continent <? Shallow Water on 
f^^^rf^v^^:^^ ip Continental Shelf Beep Water 



Fig. 41. Section of Continental Shelf 

after another, may form a h^avy deposit hmidreds of 
feet in thickness, including many shells and other relics 
of marine life. 

As new strata are added, the older strata are buried 
deeper and deeper, their grains are more or less cemented 
together by mineral substances deposited upon them by 
slowly infiltrating waters, and thus they gain a firm 
texture. It is chiefly in this way that layers of loose 
sediments are changed into layers of solid rock. 

The lowland borders of continents are often built of 
layers of sand and clay frequently containing marine 
fossils; this suggests that a former continental shelf has 
there been i-aised to a land surface. 

The shallower waters of continental shelves are of 
great importance as the chief fishing gromids of tlie 



THE OCEAN 



109 



world. The European ports around the North sea send out 
hundreds of fishing vessels to its shallow waters. The 
rich fishing grounds of the Newfoundland banks attracted 
many fishermen from the Old World over three centuries 
ago. They are still resorted to every year by fishermen 
from New England, chiefly from Gloucester, Massachusetts. 
Although far out of sight of land, the water on the banks 




Fig. 42. Orbital Movement of Water in Waves 



is so shallow that fishing schooners (such as the one shown 
in Figure 42) may ride at anchor while their men go off in 
small boats to fish with nets or with hook and Ime. Dur- 
ing fogs, which are frequent, there is danger of collision 
with transatlantic steamers, whose route leads them through 
the fishing grounds. 

79. Waves. — Wind blo"wing over the sea forms waves that 
follow the wind. The water in the waves moves only up and 
down, back and forth, with very small forward motion. The 



110 ELEMENTARY PHYSICAL GEOGRAPHY 

stronger the wind, the higher the crests and the deeper the 
troughs of the waves, the greater their length (distance from 
crest to crest), and the faster their forward motion. 

The waving of a field of grain under the wind may be 
taken as an illustration to show the relation of the curved- 
path movement of the particles to the forward progress of 
the waves. The independence of wave and water move- 
ment may be seen on a river surface when the wind is 
blowing "upstream ; or at the mouth of a harbor when the 
wind is blowing on shore, while the tide is running out. 

Great waves formed in the open ocean by gales and hur- 
ricanes are often called seas. Their height from trough to 
crest reaches 30 or 40 feet, but seldom exceeds 50 feet. 
Their length varies from 300 to 1500 feet or more, and 
their velocity from 20 to 60 miles an hour. The interval 
between the passage of successive crests, or the period 
of the wave, is seldom more than 10 or 12 seconds. 

80. The Use of Oil in Storms. — A small quantity of 
oil poured on the sea spreads rapidly and reduces the 
violence of the waves in a storm. A gale ordinarily 
forms ripples and small waves on the backs of greater 
waves and causes the crests of great seas to curl over, 
so that they would break with destructive force on the 
deck of a vessel. At such a time a film of oil decreases 
the catch of the wind on the water and prevents the large 
waves from curling and breaking. 

Many accounts of the use of oil in stomis have been 
published by the United States Hydrographic Office, 
Washington. They show that when a vessel is headed 



THE OCEAN 111 

toward the wind ("hove to") and heavy seas come on 
board over the bow, a little oil allowed to drip from a 
bag will spread even toward the wind, forming a smooth 
surface, or " slick," and the waves entering the slick will 
decrease in height and cease breaking over the deck. 

When a vessel is running with the wmd heavy seas 
sometimes come aboard over the stern ; but if a little oil 
is allowed to drip overboard, the slick spreads out like a 
fan across the wake, and the great seas are rounded off 
as they run into it, so that the vessel rides them without 
difficulty. 

81. Swell and Surf. — Great waves, traveling twenty 
to sixty miles an hour, soon run out of the storm that 
forms them and swing far across the ocean, preserving 
their length and velocity, but diminishing in height. In 
this reduced form a wave is called a swell. 

In calm weather the ocean surface may be smooth and 
glassy, but not absolutely level and quiet ; for it is never 
free from the slow heaving and sinking of fading swells 
from distant storms. A vessel becalmed in the doldrums 
always swings idly to and fro as the swell rolls by. 

When the swell runs into shoaling water close to land 
its velocity decreases, its crest rises and its trough sinks, 
thus making its height greater ; the front becomes steeper 
than the back. The swell thus becomes higher and higher 
as it advances. If it arrives on a long, smooth, gently slop- 
ing beach, the water before the advancing wave becomes so 
shallow that it cannot build up the wave front ; then the 
crest curls evenly forward in long lines nearly parallel 



112 



ELEMENTARY PHYSICAL GEOGRAPHY 



with the shore and dashes with a roaring noise upon the 
beach, in the form of surf or breakers. 

The surf is like a mill in which cobbles, gravel, and sand 
on a beach are ground finer and finer. The pebbles can 
be heard rattling as they are rolled back and forth. 




Fig. 43. Surf 

Exposed beaches may be beaten by a heavy surf, ten or 
fifteen feet high, while the neighboring sea is miruffled by 
the wind. The surf is then derived from a broad swell 
which comes from the great waves of a storm that may be 
a thousand or more miles away. 

The great hurricane of Sept. 3-12, 1889, while on its 
way from the West Indies to the Carolina coast, produced a 
destructive surf on the long beaches of New Jersey wliile the 
storm area was still a thousand miles distant. At St. Helena, 



THE OCEAN" 113 

a lonesome island in the South Atlantic, boats from vessels 
at anchor in the harbor frequently cannot reach the shore 
ill fair weather on account of the " rollers," or heavy surf, 
on the beach. The swell that produces this surf is believed 
to come from storms far away in temperate latitudes of the 
North Atlantic, 

When waves rmi upon a steep and rocky shore they 
dash unevenly against the ledges, foaming and fretting 
as they sweep back and forth. Duriiig storms spray 
may be flung up 50 or 100 feet mto the air. These great 
waves exert an enormous force, capable of moving blocks 
of rock ten or more feet in diameter. Wave work is not 
tlien limited to the immediate shore Ime ; loose materials 
in depths of ten, twenty, or more fathoms are moved about 
and gromid smaller and smaller, and the finest grindings 
are swept away to deeper, quieter water. 

82. Earthquake Waves. — When an earthquake, caused 
by some disturbance in the earth's crust, occurs beneath 
the sea the whole body of the ocean above it is moved 
slightly, and the movement then spreads away on all sides 
in long, low waves that travel with great speed. When 
nearing the shore the speed and length of the wave are 
decreased, but the height is greatly mcreased. The wave, 
may then rush far in on a lowland coast, causing great 
destruction. 

The tremendous explosive eruption of the volcanic 
island Krakatoa, between Java and Sumatra, in August, 
1883, produced waves that spread far around the world. 
Their average velocity of progression was nearly 400 miles 



114 p:lementary physical geography 

an hour. On distant coasts their rise and fall was slight, J 
but on coasts near Krakatoa the waves rushed upon the 
land with a height of from fifty to eighty feet, flooding the 
lowlands, sweeping away many villages, and drowning 
thousands of the mhabitants, A large vessel was carried 
a mile and a half inland and stranded thirty feet above sea 
level. 

An earthquake in the North Pacific produced a destruc- 
tive wave, from ten to fifty or more feet high, on the coast 
of northern Japan in the evenmg of Jmie 15, 1896. The 
coast was laid waste for 175 miles. The few persons who 
saw the wave and survived it reported that the sea first 
drew bact about a quarter of a mile and then came rushing 
in like a black wall, gleaming with phosphorescent light 
and overwhelming the shore. On the open coast the sea 
became quiet in a few minutes after the wave broke, but 
in bays the waters surged and swirled for half an hour. 
The outline of the shore was changed in many places ; 
many villages were destroyed, and thousands of acres of 
arable land were laid waste. Thousands of fisliing boats 
were crushed or carried away; 27,000 persons lost their 
lives, and 60,000 survivors were left homeless. 

83. Ocean Currents. — The upper waters of the ocean, 
to a depth of 50 or 100 fathoms, move slowly in the gen- 
eral direction of the prevalent winds, thus forming currents 
that circulate about the great oceanic areas. The general 
course of the ocean currents is such that each of the large 
oceans possesses a great eddylike current that moves 
slowly around it, leaving the central waters almost quiet. 



THE OCEAN 115 

Exercise. How many systems of eddying ciirrents are shown in 
Figure 44 ? Which one is the largest ? Which tlu'ee smaller ones 
are of about the same size ? In wha,t ways are the eddying currents 
alike ? In what diif erent ? Compare their movements along the west 
coasts in middle latitudes ; along east coasts. How do they move 
near the equator? Note the long equatorial countercurrent in the 
Pacific, separating the two great eddies, north and south. Note the 
connecting current between the two eddies of the Atlantic. Compare 
the general courses of the winds, Figures '22 and 23, with the courses 
of the ocean currents. Name some districts where the winds and 
currents agi-ee. 

The remarkable correspondence between the course of 
the oceanic eddies, Figure 44, and the course of the pre- 
vailing winds over the oceans, as shown in the charts, 
Figures 22 and 23, points to the winds as the cause of the 
currents. Like the circulation of the atmosphere, the eddy- 
mg of the upper waters of the oceans must be regarded as 
a characteristic of a globe having large oceans, a mobile 
atmosphere, and a warm equatorial zone. 

The belief that the winds cause the currents is confirmed 
by the way in which the surface drift of the waters may be 
for a time brushed to one side of its usual course, or even 
reversed, during a storm. 

If an observer stood in the center of an oceanic eddy in 
the northern hemisphere, the currents would pass around 
him from left to right, or clockwise; in the southern 
hemisphere, from right to left, or counter-clockwise. 

The eddying currents are the chief natural basis for sub- 
dividing the great oceanic area into the six oceans; the 
North and South Pacific, the North and South Atlantic, 
and the Indian oceans each having its own great eddy, 



116 



ELEMENTARY PHYSICAL GEOGRAPHY 



while the Antarctic ocean has a great eddy around the 
south pole, joining the eddies of the three southern oceans. 
The Arctic also has a current about the pole joining that 
of the North Atlantic, somewhat like the two loops of a 
figure 8 ; but the Arctic should be classified as a large sea 
or gulf rather than as an ocean. 

A broad and shallow current that advances at a rate of 
ten. or fifteen miles a day, like that which crosses the 

middle North Atlantic, 
should be called a drift. 
A narrow current, flow- 
ing with a velocity of 
fifty or more miles a day, 
like that issuing from 
the Gulf of Mexico 
through the Strait of 
Florida, should be called 
a stream. 
It is important that the masters of vessels should be 
acquainted with the movements of ocean currents. In 
cloudy and foggy weather, when observations of the sun 
cannot be made to determine latitude and longitude, 
a vessel might be drifted out of its expected course 
if no allowance were made for the movement of the 
waters. Thus, if a vessel intending to follow the course 
3IabcN., Figure 45, were drifted to the course 3IABCE, 
it would pass dangerously near the headlands at B and C, 
and might even run ashore. Wrecks on the south- 
west coast of Ireland have not infrequently been due 
to this cause. 




Fig. 45. 



Displacement of a Vessel by 
Currents 



THE OCEAN 



117 



In Nansen's famous attempt to reach the north pole he 
sailed eastward along the northern coast of Asia and 
turned northward into a region of ice fields, where his 
vessel was caught between two floes. He then drifted 
with the ice, expecting that the Arctic current would 
carry him past the pole toward Greenland. Had he gone 
further east before ^^^ 
turning north, a closer 
approach to the pole 
might have been made. 

The drift of aban- 
doned wrecks, whose 
positions are noted by 
passing vessels, gives 
indications of the 
movements of 
rents. The 
lines in Figure 46 
show the drift of sev- 
eral wrecks. Tlie broken lines indicate the drift of many 
logs from a great timber raft that was abandoned in a 
storm while on the way from the Canadian provinces to 
New York, December, 1887. 

Thousands of bottles have been thrown into the sea, with 
record of the time and place where they have been set adrift 
and request that the finder shall report the time and place 
of their discovery, afloat or ashore. The dotted lines of 
Figure 46 give a few inferred "bottle tracks." 

The several parts of the vai'ious eddies may receive spe- 
cial names. Those parts which run westward, near and 



cur- 
angular 




Fig. 46. 



Drift of Floating Objects by 
Currents 



118 ELEMENTARY PHYSICAL GEOGRAPHY 

about parallel to the equator, are called the equatorial cur 
rents. The eastern part of the South Pacific eddy is called 
the Humboldt, or Peruvian, current; it brings a great body 
of cool water from far southern latitudes. 

The name Gulf Stream, m the Atlantic, should be lim- 
ited to the narrow, deep, and rapid current which issues 
from the Gulf of Mexico with a velocity of eighty miles 
a day; the name is popularly, but incorrectly, extended 
far northeast over the broad, shallow, and slow-moving 
drift on the northern side of the North Atlantic eddy, and 
even along its branch, past Norway. This extension of the 
current is not a stream at all, and it includes much water 
that passed outside of the West Indies and not through 
the Gulf of Mexico. 

Sailing vessels should take advantage of winds and cur- 
rents m shaping their courses. If bound from the eastern 
United States to far South American ports, they should 
cross the equator well to the eastward, so as to avoid being 
carried backward by a strong current past the Guiana coast, 
where the winds may fail in the doldrums. A ship sailing 
from an Atlantic port to Australia should romid Cape of 
Good Hope and take advantage of favorable wuids and 
currents in the southern Indian ocean about latitude 50°. 
On the homeward voyage favoring winds and currents 
would be found in the same latitude of the South Pacific, 
toward Cape Horn. 

84. Currents and Temperatures. — Currents influence 
the distribution of temperature in the oceans and in the 
winds that blow over tliem. In the North Atlantic, for 



THE OCEAN 119 

example, a broad drift of rather warm water flows north- 
east in middle latitudes, past the British Isles and Nor- 
way; while a cold current returning from the Arctic regions 
flows southward past Labrador and Newfoundland. Hence, 
in the same latitude, winds from the sea are mild in north- 
western Europe and chilling in northeastern America. 

In winter the harbors of the Labrador and Greenland 
coast are closed with ice ; harbors in the same latitude on 
tlie eastern side of the Atlantic remain open all the year 
round. In what countries are these harbors situated? 
Northern Norway has a milder climate than any other 
country at so great a distance from the equator. Why 
is this ? What land in the southern hemisphere is as 
far from the equator as Norway? 

The southern coast of Alaska has a comparatively mild 
climate on accomit of the northeastward drift of the sur- 
face waters in the North Pacific eddy. The cool Peruvian 
current keeps the temperature so low about the Galapagos 
islands (near the equator west of Peru) that coral reefs, 
such as abound further west m the equatorial Pacific, 
are not found on their shore. 

85. Tides. ^ Regular movements of the ocean, rising 
and falling on the shores twice in a little more than a day 
(twenty-four hours, fifty-two minutes), are called tides. In 
the open- ocean tides are not perceived ; but in many bays 
the tidal change of level, or range, reaches ten, twenty, or 
more feet. The highest stage of the tide is called high tide 
or high water; the lowest stage, low tide or low water. 
The change of level is accompanied by currents, — flood tide 



120 



ELEMENTARY PHYSICAL GEOGRAPHY 



running in from the ocean, ebb tide running out again. A 
brief period of quiet, or " slack water," occurs when flood 
changes to ebb, or ebb to flood. The vessels that are aground 
at low tide in Figure 47 would be afloat at high tide. 




Fig. 47. Low Tide in a Harbor 

The tidal undulations of the oceans are caused chiefly by 
the attraction of the moon ; they are somewhat affected by 
the attraction of the sun. 

Tidal currents are beneficial in maintaining a circulation 
in bays and harbors where the waters might otherAvise be 
almost stagnant. At high water a harbor will admit ves- 
sels of a larger size than could enter if the ocean level 
did not change ; but at low water the harbor may be inac- 
cessible except to much smaller vessels. The hour of 
departure of ocean steamers is usually determined by the 



THE OCEAN 



121 



hour of high tide, so that they may have water as deep as 
possible when leaving their harbor. 

In funnel-shaped bays or estuaries tlie tidal range 
becomes large, and flood and ebb currents are very strong, 
making navigation dijfficult or even dangerous. The tidal 
range sometimes exceeds fifty feet in the estuaries at the 
head of the Bristol channel in western England, and of 
the Bay of Fundy in Nova Scotia ; in the latter the flood 




Fig. 48. The Tidal Wave, or Bore, in tiie Seine 

current rushes in like foaming surf, shown in Plate V. 
The estuary of the Seine in northwestern France has a 
similar surf-like tide, shown in Figure 48. Such surf-like 
tides are called bores. A bore occurs at the mouth of the 
Amazon; it is so violent on the northern side of the river 
near the sea that the shore line is rapidly worn back, and 
hence no important settlements have been made there. 

Where tidal currents are thus strengthened they sweep 
the sediments of the shallow bottom back and forth, 
grinding them finer and finer. The finest particles thus 



122 



ELEMENTARY PHYSICAL GEOGRAPHY 



produced are slowly drifted offshore, where they settle in 
deep water. When a gale is blowing and producing 
waves in strong flood or ebb currents their work on the bot- 
tom is much increased ; for the sediments are slightly raised 
from the bottom by the agitation of the waves, and thus 
they are brought more into the power of the tidal currents. 

Many curious tidal phe- 
nomena are found on shore 
lines of different forms. 
At New York a high tide 
entering from the harbor 
reaches the rocky narrows 
of Hell Gate when a low 
tide arrives through Long 
Island sound ; and six 
hours later a low tide 
from the harbor meets a 
high tide from the sound. 
Thus a rapid current is 
caused to flow back and 
forth in the narrow pas- 
sage, which was danger- 
ous to vessels until the channel was widened by blasting 
away its reefs. A current of this kind is sometimes called 
a tidal race. 




Fig. 49. Jellyfish floating in Sea Water 



86. Life in the Ocean. — The surface layers of the open 
ocean possess a considerable variety of animal life, from 
large mammals, like whales, to minute organisms, Figure 
40, whose tiny shells are so plentifully strewn over the 



THE OCEAN 



123 







Fig. 50. Deep-Sea Fish, x 



ocean floor. The former occur in moderate numbers ; the 

latter are countless. The distribution of surface life is 

determined chiefly by differences of temperature from the 

torrid to the 

frigid zones. 

Those forms 

which swim 

or are drifted 

freely by the currents are found over vast areas. In fair 

weather the surface waters are sometimes alive with minute 

jellylike forms. 

The nearly quiet water about the central part of the 
great eddying currents generally contains a considerable 
quantity of floating seaweed, or sar- 
gassum ; hence these central areas are 
called sargasso seas. The sargassum is 
believed to be derived from shore 
waters, where it grows on the shallow 
bottom. A great variety of small ani- 
mals live on the floating w^eed, and a 
certain kind of fish uses the weed as 
a "nest" for its eggs. 

The intermediate depths of the 
ocean, between the upper part and 
the bottom, are prevailingly without 
life, — a great desert space, cold, quiet, 
and monotonous. 
The deep ocean floors have no plants. They are inhab- 
ited by a considerable variety of animals, such as fish, 
crabs, shellfish, starfish, etc. ; but the forms of life are 




Fig. 51 
Deep-Sea Crustacean, x \ 



124 ELEMENTARY PHYSICAL GEOGRAPHY 

here much less varied and less numerous than in the 
shallower waters near the shore. 

While many deep-sea animals are blind, it is curious 
that some have well-formed eyes and are ornamented with 
colors. Colors would be useless if they could not be seen, 
and eyes would be of no service in complete darkness. 
Hence there must be some light in the ocean abysses. As 
sunlight cannot penetrate to great depths, the light may 
be supplied by phosphorescent animals, of which there 
are many kinds in the deep sea. 

The shallow waters of the ocean margin teem with plants 
and animals. Many animals, such as sponges, corals, and 
barnacles, are fixed to the bottom; they need not move 
about in search of food, because the moving waters bring 
it to them. Nearly all the plants of the sea are of a com- 
paratively simple kind, without flowers or seeds. The 
shallow waters are the fishing grounds of the sea and fur- 
nish important supplies of food to the neighboring lands. 

Supplement to Chapter III 

87. The Cause of the Tides. — Note the time when the moon 
passes over the south point of the horizon on two successive days. 
(These observations may be made in the early evening when the 
moon is near its first quarter. If daytime obsei-vations are pre- 
ferred, they may be made in the early forenoon when the moon is 
between third quarter and new; or in the late afternoon between 
new moon and first quarter.) How long is the interval between the 
two passages ? Compare this interval with that between two high 
tides, as stated on page 119. How are the two intervals related? 

The above comparison shows that the tides in some way depend 
on the moon, because two sets of tides occur in the time (24 hours 



THE OCEAN 



125 




Fig. 53 



1st Day 
New Moon 



ljC^l' d) 



M) 
Spring Tides 



^ 



52 minutes) between two successive passages of the moon across the 
meridian. It can be shoAvn that the attraction of the moon on the 
oceans tends to cause high tides, H' 
and //", Figure 52, on opposite sides 
of the earth near the equator, with low 
tides, 0' and 0", between them. The//" 
tides tend to preserve a constant posi- 
tion with respect to the moon, some- 

vvliat as indicated in the figure. Hence as the earth turns round 

(the axis standing at right angles to 
the paper), any point in the equa- 
torial oceans must pass H', 0', H", 
0" in 24 hours 52 minutes, and 
must therefore experience two high 
and two low tides in that period. 
The moon tends to form similar 
but weaker tides around all the lati- 
tude circles in the two hemispheres. 
The sun also tends to cause tides ; 
but in spite of the vastly greater 
size of the sun than of the moon, 
the sun is so much farther away 
that the solar (sun) tides have only 
about one third of the strength of 
the lunar (moon) tides. 

At new moon, when the sun and 

moon are on the same side of the 

earth, as in Figure 53, the lunar (i) 

and solar (S) tides act together, and 

hence the rise and fall of the tides, 

or the tidal range, is increased. At 

first quarter the line to the moon is 

*^" at right angles to that to the sun, 

as in Figure 54. Here the sun tries to make a low tide where the 

moon makes a high tide, L ; and the moon makes a low tide where 




<? 




7th Day 
first Quarter 



■r ■ Neap Tides 

Fig: 54 

11th Day 
S' Full Moon 

i" 

Spring Tides 

Fig. 55 

' 21st Day 
Third Quarter 



Neap Tides 



@H 



126 



ELEMENTARY PHYSICAL GEOGRAPHY 



the sun tries to make a high tide, S. As a result, the tidal range 
is weakened. How do the lunar and solar tides combine at time of 
full moon, Figure 55 ? at time of third quarter. Figure 56 ? 

It thus appears that in the twenty-eight days between two new 
moons, or about a month, the tidal range is strong, weak, strong, and 
weak. At the times of strong range the tides are called spring tides ; 
at times of weak range, neap tides. The variation of tidal range 
from new moon to fuU moon is shown in Figure 57. How often 
does the period of spring tides occur in a month ? of neap tides ? 

It is not possible at present to state how the tides behaA^e in the 
open ocean ; they cannot be observed in deep water, far from shore. 




Fig. 57. Variation of Tides for Two Weeks 



They are known only as they come upon the shores of islands and 
continents. Their strength then depends not only on the combina- 
tion of lunar and solar forces, as in spring tides and neap tides, but 
still more on the form of the shallowing sea floor and of the shore 
line. Just as swell is increased in height as it runs ashore, so are 
the tides; for the tides are in reality very long, low waves; but 
while the surf caused by the arrival of successive swells may roll in 
on a beach every five or ten seconds, the high tide rolls in only every 
12 hours 26 minutes. Its strength is usually less on headlands than 
in bay heads. 



THE OCEAN 127 



QUESTIONS 

Secs. 68, 69. What is the ocean? Compare the Arctic and Ant- 
arctic oceans. Locate the poles of the land and water hemispheres. 
Consider the ocean as a highway. 

70, 71. Compare the earlier and later objects of ocean exploration. 
Describe the method of deep sounding. What is a water bottle ? a 
dredge ? How are nets used in sounding ? Where are the places of 
greatest depth in the ocean ? About how deep are they ? 

72, 73. What mineral substances are dissolved in ocean water? 
What is their source? What gases are dissolved in ocean water? 
What purpose does one of these gases serve ? What is the density 
of ocean water ? What amount of dissolved substances does it con- 
tain ? Compare the ocean and the atmosphere. Describe the colors of 
the ocean under different conditions. What causes pliosphorescence ? 

74. Describe the distribution of temperature at the ocean surface ; 
at the ocean bottom.. How do ocean temperatures vary through the 
year? How deep does sunshine penetrate the ocean? Compai-e the 
effect of changing temperature on the density of fresh water ; of 
salt water. How is the cold water at the bottom of the equatorial 
oceans accounted for? 

75. Why does ice float? What is floe ice? pack ice? What are 
icebergs ? What size do they reach ? How do they float ? Where 
are they seen ? What is their source ? 

76. Describe the deep ocean bottom. What is the character and 
source of ocean-bottom materials ? What can you say of mountains 
and volcanoes in the ocean ? 

77. What is a mediterranean? Name the chief examples. How 
does their temperature differ from that of the oceans ? 

78. What is a continental shelf? Give some examples. What 
materials are found on continental shelves? How are stratified 
deposits formed ? What do they include ? How may they be 
changed to rock ? Of what value to man are the shallow waters 
of continental shelves? 



128 ELEMENTARY PHYSICAL GEOGRAPHY 

79, 80. What are waves ? What size do they reach ? How do 
they move? IHustrate the difference of wave movement and water 
movement. What effect has oil on waves? 

81, 82. What changes of form do waves suffer? What is swell? 
surf? Why does surf fall forward? What are "rollers"? What 
work is done by waves ? To what depth may they act ? What is an 
earthquake wave ? Describe two examples. 

83. What are ocean currents ? What is their general movement ? 
What divisions of the ocean are suggested by its eddying cm-rents ? 
What is a drift? a stream? Of what practical importance is a 
knowledge of ocean currents? How are ocean currents determined? 
What is the cause of ocean currents ? How is this proved ? Name 
and describe some important members of the oceanic eddies.. To 
what should the name Gulf Stream be limited ? How may sailing 
vessels take advantage of winds and currents? 

84. How do ocean currents influence the distribution of tempera- 
ture ? Give examples from Labrador, Great Britain, Alaska, Peru. 

85. What are the tides? Define high tide, low tide, slack 
water, flood, ebb. How are tides caused? What practical bene- 
fits arise from them ? What inconveniences ? What is tidal range ? 
What may it amount to ? Where does strong range occur ? What 
is a tidal bore ? What work is done by tidal currents ? When is this 
work most effective? What is a tidal race? Give an example. 

86. Consider the distribution of life in the ocean surface waters. 
How is it chiefly controlled? AVhat is a sargasso sea? What can 
you say about the intermediate depths ? the bottom ? What can be 
inferred from the color and eyes of deep-sea animals ? Consider the 
distribution of life in the shallow marginal waters. 



CHAPTER IV 
THE LANDS 

88. Area of the Lands. — The globular earth is uneven 
enough to raise somewhat more than a quarter of its sur- 
face slightly above the oceans in broad land areas, called 
continents. 

The area of the globe is about 197,000,000 square miles. 
The lands occupy somewhat more than 50,000,000 square 
miles ; their total area remains uncertain until the polar 
regions are fully explored. Six sevenths of the land area 
are in the land hemisphere (see Figure 34), where the 
ocean occupies little more than half the surface. The 
lands in the water hemisphere occupy only about one 
fifteenth of the surface. 

89. The Continents. — There are five large bodies of 
land, known as continents. Europe and Asia together 
form a single continent, often called Eurasia, the largest 
of the five. On account of the great extent of this 
continent, and still more because of its varied relations to 
human history, it is convenient to describe both Europe 
and Asia as a "grand division" of land. 

The other continents are Africa, North and South 
America, and Australia,- the last being the smallest of 
the five. It is possible that the lands of the Antarctic 

129 



130 ELEMENTARY PHYSICAL GEOGRAPHY 

regions may be discovered to be large enough to rank as 
a continent; but little is known of them at present. 

The five continents differ greatly in size, outline, 
arrangement of parts, and degree of sej)aration. The 
most remarkable fact concerning their distribution over 
the earth's surface is that they cluster around the Arctic 
circle, inclosing the Arctic ocean, and thence extend far 
southward, narrowing toward their ends in the great ocean 
of the southern hemisphere. The narrow North Atlantic 
and the much narrower Bering strait occupy only about one 
ninth of the Arctic circle ; the rest of its circuit crosses 
the lands, with a few narrow arms of the sea that separate 
some of the Arctic islands from North America. 

South America lies southward of North America ; 
Africa lies southward of western Eurasia; Australia lies 
southward of eastern Eurasia. None of these southern 
continents reach the parallel of 60° south latitude ; the 
whole circuit of this parallel lies on the ocean. 

Another remarkable feature in the distribution of the 
lands is that two land areas are seldom found opposite 
to each other, on opposite sides of the earth. Oj^posed 
to each continent is generally an ocean surface, as may be 
seen by examining a globe. 

A third remarkable feature regarding the distribution 
of the lands is that, excepting Australia and the possible 
Antarctic continent, nearly all the other lands are found 
on one half of the earth's surface, known as the land hemi- 
sphere. (See page 96.) 

Eurasia and Africa are often called the Old World, 
because parts of them have been known to the people of 



thp: lands 131 

our race for more than twenty centuries ; while North and 
South America are called the New World, because they 
have been known to us for only a little more than five 
centuries. But these names are appropriate only from 
the point of view of human history. Both the Old and 
the New Worlds, so called, contain so much very ancient 
land, raised above the ocean in early stages of the earth's 
history, and so many mountains and plams that have been 
formed in the later stages of the earth's history, that 
neither world should be regarded as, on the whole, older 
or younger than the other. 

The greatest islands are comparatively near the conti- 
nents, as in the archipelago north of North America, the 
West Indies, Newfoundland, the British Isles, Madagas- 
car, the Japanese islands, the Malayan-Australasian archi- 
pelago, and New Zealand. Most of these islands stand 
upon continental shelves and are separated from the con- 
tinents only by comparatively shallow water; but New 
Zealand is separated from Australia by deep water. The 
numerous oceanic islands, distant from continents, are of 
small total area (about 40,000 square miles). 

90. Height of the Lands. — The highest mountain peaks 
(25,000 to 29,000 feet) do not rise above sea level so much 
as the greatest ocean depths sink below it (31,600 feet). 
The average elevation of the lands (2400 feet, less than 
half a mile) is much less than the average depth of the 
oceans (about two miles). 

Figure 58 exhibits the proportion of high and low land, 
and of deep and shallow ocean, the whole area of the earth 



132 



ELEMENTARY PHYSICAL GEOGRAPHY 



'being measured by the breadth of the figure. It is thus-seen 
that most of the land surface is but little above sea level, 
^hile most of the sea floor lies deep below the sea surface. 



91. Changes of Continental Outline. — The form of the 
lands and the outline of their shores seem at first sight to 
be unchangeable. But the more the world is studied, the 
more certain it becomes that very slow movements are 

going on in the 



FEET 
30,000 



20,000 



10,000 



20,000 




Fig. 5tS. Height of Land and Depth of Sea 



METERS 

[-8,000 earth s crust, 
and that the out- 
■4,000 line of the con- 
tinents is sub- 
ject to change 
as the conti- 
*'°"" nental masses 
very slowly rise 
or sink. The 
movements are 
so slow that 
they are hardly perceptible in the course of a century ; 
but when continued for hundreds of centuries they cause 
changes of great importance in the geography of the lands. 
Observations in the last hundred years or more give 
reason to believe that the coasts of Massachusetts and 
New Jersey are now sinking (one or two feet a century), 
and that much of the coast of Sweden is rising (greatest 
rise, three feet a century). The coast of the Netherlands 
is sinking a foot a century, and its fields near the shore, 
fifteen to twenty feet below the sea level, are diked to keep 



THE LANDS 133 

the water off. Canada northeast of the Great lakes is 
rising, so that the waters of the lakes are slowly backing 
up on their southwestern shores. 

Widespread layers of rock containing fossils of sea 
animals are found on various parts of the continents, show- 
ing that these parts of the lands have, in some ancient 
time, been beneath the sea. Many other proofs of change 
of level will be given on later pages. 

92. Varied Conditions on the Land Surface. — The sur- 
face of the continents possesses great variety of form and 
composition, very unlike the monotony of the broad and 
deep sea floors. Rocks and soils, as well as mountains, 
valleys, and plains, differ greatly from place to place. 

Mountain ranges are characteristic of the continents 
rather than of the sea floors, where plains of vast extent 
prevail. But mountain ranges occasionally rise from the 
sea bottom, showing their crests above the surface, as in 
the West Indies. Volcanoes and their lavas are among 
the few features possessed in common by the deep sea 
and the dry lands. 

The continental shelves, overlapped by some of the 
oceans, have something of the variety of the lands from 
which they receive washings of gravel, sand, and clay. 

While the deep-sea floor is always wet, dark, cold, and 
quiet, the land surface has many different kinds of weather 
and climate. Heav}'- rains are followed by clear sky; 
strong winds, by light winds or calms. A bare desert 
surface in the torrid zone may be heated at noon above 
130°, and may cool nearly to freezing the next night. In 



134 ELEMENTARY PHYSICAL GEOGRAPHY 

the frigid zone the frozen soil may warm and thaw at the 
surface during summer, but it will be frozen again, even 
to 80° below zero, the next winter. 

Variations of temperature, so distinct on the land sur- 
face, rapidly decrease underground. At a depth of four 
or five feet daily changes are hardly perceptible ; at a depth 
of twenty or thirty feet there is but little variation from 
the mean temperature of the year (about 80° in the torrid 
zone, near zero in far northern lands). 

In northeastern Siberia, where the ground is frozen to a 
depth of 300 to 500 feet, grass and bushes grow when the 
soil thaws for a few feet in summer; but large trees are 
wanting. The mammoth, an ancient animal resembling a 
hairy elephant, but no longer found living, has on account 
of the extreme cold sometimes been preserved in the beds 
of sand and gravel that border some of the Siberian rivers, 
where it was buried at the time of river floods many 
centuries ago, and afterward frozen. 

93. Activities of the Lands. — In nothing do the conti- 
nents differ more strikingly from the deep-sea floors than 
in the activity of the various processes that go on upon 
the lands, and in the changes that the processes produce. 
The surface rocks split apart when water freezes in their 
crevices, or they slowly rust and decay under the action 
of air and water. A sheet of loosened rock waste is 
thus formed over most of the land surface. The various 
processes by which rock waste is produced are known 
under the general term weathering. Weathering varies 
greatly under different climates and with different rocks. 






THE LANDS 



135 



Every rock-ledge or quarry offers opportunity for observ- 
ing the widespread process of weathering. The weathering 
of the older gravestones in cemeteries may frequently be 
noticed. In cities the different amounts of weathering on 
old and new stone buildings, or in buildings of different 
kinds of stone, serve to illustrate in a simple way the 
changes that occur on 
a much greater scale 
all over the lands. 

In the dry, mild, 
and equable climate 
of Egypt ancient 
statues have been but 
slightly weathered in 
several thousand 
years. A great stone 
monument, sixty feet 
high, known as Cleo- 
patra's Needle, 
Ijrought from Egypt 
to New York in 1880, was so much affected by the weather 
in a single winter that it became necessary to coat its sur- 
face with a i)reservative substance. In Egypt it had stood 
over 3000 years with little change. 

In regions of plentiful rainfall and abundant vegetation 
weathering advances with comparative rapidity, and a deep 
soil is formed; solid rock may not be found for fifty or more 
feet below the surface. In high latitudes, where the tem- 
perature frequently rises and fails past the freezing point, 
frost is active in splitting rock masses into fragments. 




Fig. 59. A Quarry showing Weathered Rock 



136 ELEMENTARY PHYSICAL GEOGRArHY 

94. The Wasting of the Lands. — Surface water, supplied 
by rain or melting snow, washes the finer rock waste clown 
the slope of the land to the valley floors or to the streams, 
and the streams bear the waste along their channels, thus 
sweeping it from one place and spreading it over another, 
or washing it to the sea. Where streams run they rasp 
their channels with the rock grains that they bear along, 
and valleys are thus slowly Avorn in the surface of the land. 
The higher the land, the deeper the valleys may be cut. 

The longer the period of wasting and washing, the more 
material is taken from the valley sides and the wider and 
more open the valleys become. 

Lai'ge valleys, receiving many smaller branching valleys 
and ravines that dissect the surface of the land and lead 
streams from higher to lower ground, are among the most 
characteristic features of the continents. Valleys are the 
result of stream action and do not occur on the deep-sea 
floor. They are sometimes found beneath sea level, extend- 
ing forward from the present coast line across the shallow 
continental shelf ; they are then taken as proof of the 
lowering of that part of the continent. 

The winds act with great effect on bare surfaces, sweep- 
ing finer rock waste into drifts (dunes), and raising the 
dust aloft to settle far away. The waves, currents, and 
tides of the ocean wear the edge of the land and the 
shallow continental margins, cutting cliffs and building 
sand reefs along the shores, and sweeping away the finer 
land waste. 

The general process of wasting and washing, by which 
the land surface is slowly worn down and the deeper 



THE LANDS 137 

structures of the earth's crust are attacked, is called denu- 
dation or erosion. The movement of land waste from one 
place to another by various agents (streams, currents, 
winds, waves, etc.) is called transportation. The process 
of laying down land waste on valley floors, in lake basins, 
and on sea floors is called deposition. 

Illustrations of these various processes may be found 
on a small scale in the neighborhood of many schools. 
The wet-weather streams of roadsides and the waves in 
ponds or reservoirs exhibit in a small way the processes of 
erosion and transportation in large rivers and oceans. The 
strong action of winds on dusty roads and their lack of 
effect on the ground beneath grass or forests illustrate the 
contrast that prevails between wind action in dry and in 
moist regions. 

The difference between the conditions that prevail on 
the land surface and on the sea floor is thus seen to be 
very great. The sea floor is enduringly quiet and silent. 
The tides of the deep sea are very faint. The creeping 
. of cold polar water toward the equator must be almost 
imperceptible. The gain of the bottom by the steady 
shower of organic remains from the surface is very feeble, 
and the change of form by this gain must be exceedingly 
slow. 

Although the changes caused in the form of the lands 
by weathering and washing are gradual, they have been so 
long continued that marA^elous results have been produced. 
Not only are the lands deeply dissected where valleys have 
been worn in plateaus and mountains, but whole mountain 
ranges have been worn down to lowlands. The forms of 



138 ELEMENTARY PHYSICAL GEOGRAPHY 

the land to-day can be appreciated only when it is seen 
that they are the present stage of a long series of changes. 
The description and explanation of land forms thus con- 
sidered is the object of most of the remainder of this book. 

The general wasting of a land surface is slow, but local 
changes are easily noted by the attentive observer. Slop- 
ing fields and roads are gullied by wet-weather streams. 
Much soil may be washed from a plowed hillside in a 
single rain storm. Landslides produce striking changes 
on mountain slopes and in the valleys below. Cataracts 
like Niagara wear back their cliffs more than a foot a 
year. 

The land waste that is washed down a valley is deposited 
at the mouth of the stream in a lake or the sea, and thus 
the land is built out, forming a delta, which may grow 
forward perceptibly in a century. Ostia, once the port of 
ancient Rome, is now over a mile inland from the advanc- 
ing front of the Tiber delta. Sea cliffs may be cut back 
by the waves ; part of the exposed eastern bluff of Cape 
Cod, Massachusetts, is retreating at an average rate of 
three feet a year. 

The rate of erosion on the lands varies greatly with rock 
structure, slope, and climate. The Mississippi carries 
enough land waste to lower its whole basin an inch in about 
three centuries. An inch in from one to ten centuries 
may be taken as a rough measure of erosion, averaged 
for large areas. 

95. Useful Products of the Lands. — The rock of the 
earth's crust in the lands is of great service in building and 



THE LANDS 139 

road making ; hence it is often quarried. Clay is burned 
to make bricks, used in building and street paving. Lime- 
stone when heated ("burned") is changed to lime, used 
in making mortar. Coal, found in layers between strata 
of clays and sandstones, is the most useful kind of fuel. 
Rock oil, or petroleum, is of great value as a fuel for 
lamps, and in many other ways. The ores of many metals 
are mined and smelted, to supply man's needs ; iron, copper, 
lead, tin, and zinc are the most useful metals in manufac- 
tures ; gold and silver are used as money and in the arts. 
Precious stones or gems, such as the diamond, ruby, and 
emerald, are highly prized for their beauty and rarity. 

All these products of the lands play an important part 
in the advance of civilization. Spain has iron ore but no 
coal. England has abundant coal and irDn ore. How is 
the present condition of these two comitries affected by 
the presence and absence of coal supply? The United 
States possesses extensive coal fields and abundant deposits 
of iron ore, as well as other mineral products in great 
variety. Argentina possesses relatively little mineral 
wealth. What comparison can you make between these 
two countries in other respects ? 

QUESTIONS 

Secs. 88, 89, 90. What is the area of the globe? of the lands? 
State three remarkable facts concerning the distribution of the 
lands. Why are the terms Old World and New World not appro- 
priate in physical geography? State the relation of the larger 
islands to the continents. Compare land heights and ocean depths. 
State the pK)portion of high land to deep ocean. 



140 ELEMENTARY PHYSICAL GEOGRAPHY 

91. What changes are taking place in continental outline ? Give 
some examples. 

92. Contrast the land surface and the sea floor as to form ; as 
to changes of temperature. Contrast the distribution of mountain 
chains and of volcanoes. How does temperature vary underground ? 
Describe the effects of extreme cold in northeastern Siberia. 

93. What changes take place on the lands? What is weather- 
ing? Give examples of it. Name some of its effects. How does 
frost act and where is it most effective ? 

94. Describe the action of streams. How are the depth and 
width of valleys determined? Why are valleys characteristic of the 
lands? How are the lands affected by the winds? by waves and 
tides? Define denudation. What effects of erosion have you seen? 
State the effects of long-continued erosion. W^hat changes have 
occurred on shore lines ? Upon what does the rate of erosion 
depend? What is its average rate? 

95. What are Some of the useful products of the earth's crust? 
What comparison can you make between England and Spain? 
between the United States and Argentina? 



CHAPTER V 
PLAINS AND PLATEAUS 

96. Introductory Example. — In certain parts of the 
world the hills bordering a mountain range descend directly 
to the seashore. Rock waste is washed from the moun- 
tain slopes and carried down the vallejs by streams. The 
larofer rivers build deltas at their mouths, and here the sea 
is bordered by low land. Waves beat on the coast and 
cut cliffs in the headlands between the valleys; here the 
sea is bordered by high land. The waste of the land is 
spread over the neighboring sea floor by waves and currents. 

Figure 60 is a picture of a model representing a region 
of this kind. Momitains and ridges of varied form descend 
toward the shore line. A river in a large central valley 
receives the streams with their rock waste from a number 
of branching valleys and has built a delta at its mouth. 
This means that while the land has been eroded and 
roughened by the action of weather and streams the sea 
floor has been smoothed by the gain of land waste. The 
depth and number of the valleys show that already m-uch 
waste has been carried into the neighboring sea. The 
dredge brings up gravel, sand, and mud from the sea bot- 
tom, the sediments usually being of finer grain as distance 
from land and depth of water increase. 

141 



142 



ELEMEXTARY PHYSICAL GEOGRAPHY 



Figure 61 is a map of part of the mountains shown in Figure 60. 
The form of the ridges is here indicated by short lines, called hachure 




Fig. 60. Mountains bordering the Sea 



lines, which show the direction in which the slopes descend. Gentle 
slopes may be represented by long fine lines, steep slopes by short 
heavier lines. This map may serve as a sample for a number of others 
that should be drawn from the 
figures on later pages. 



A rugged land like that 
of Figure 60 seldom sup- 
ports a large population, 
for it is not easy to gain 
a living on steep moun- 
tain sides. It is only in 
the valleys that strips of 
flat land, suitable for easy 
occupation, can be found. 
Most of the population in 
such a region is gathered 




Fig. til. 



Sample Map of a Mountainous 
Coast 



PLAINS AND PLATEAUS 143 

in villages near the mouths of the large rivers, where the 
valleys are wider and the ridges between them are lower. 
Roads cannot easily follow the shore, for many of the cliffs 
are washed to their base at every high tide. In jjassing 
from one valley village to another the traveler must climb 
over a ridge; this is hard work and it discourages settle- 
ment. Many dwellers in the shore villages are seafarers 
and fishermen, although there are few protected harbors, 
for the shore line is coinpai-atively straight. 

The coast of California presents many stretches of this 
kind. The Sierra Santa Lucia, south of Monterey, descends 
boldly to the sea, its spurs being cut off in great cliffs. 
The shore is harborless and thinly inhabited for a distance 
of seventy miles. 

97. Narrow Coastal Plains. — There are some regions 
where the foothills of the mountains descend to a lowland, 
and the lowland slopes gently forward to the sea. Such a 
lowland is called a coastal plain. The gentle slope of the 
lowland is continued in the slowly deepening sea floor. 
Tlie form of the land is here much more favorable to 
human occupation than in tlie previous example. 

Plams of this kind are often divided into many simi- 
lar strips by the shallow valleys of streams that flow 
"across them from the mountains. Each strip of the plain 
is so smooth and so nearly level that a great part of the 
rainfall enters the open soil, instead of running off in 
streams. The plain is built of layers or strata of gravel, 
sand, and clay, the uppermost layer or stratum forming 
the surface of the plain. The pebbles of the gravel often 



144 



ELEMENTARY PHYSICAL GEOGRAPHY 



resemble the harder rocks of the hilly background; the' 
clay often contams shells like those living in the sea. 
Figure 62 shows a region of this kind. 

Trace the line between the mountains and the coastal plain in 
Figure 62. How many streams are seen crossing the plain? AVhich 
stream has the broadest valley? Why? Compare the depth of the 
valleys in the jilain with that of the valleys in the mountains. 




Fig. 62. Narrow Coastal Plain 



and some of the hills bordering its inner margin. Notice that in j 
the figure the streams crossing the plain are foreshortened, while 
the spaces between the streams ai-e on true scale. Figure 63 illus- 
trates the way in which the map should be drawn. 

Little ravines have been eroded by wet-weather streams 
in the side slopes of the plain bordering the valleys. Even 
the larger valleys have been slowly eroded by the rivers 
that flow through them. In the future the plain will be 



PLAINS AND PLATEAUS 



145 



more carved or dissected ; in the past it was less dissected. 
Before any valleys were cut the different parts of the plain 
were all united in a continuous, even surface. 

In view of all this, it must be concluded that the coastal 
plain in Figure 62 was once part of a shallow sea bottom 
and that this region was 
then like the sea-skirted 
mountains of Figure 60. 
Since then the relative 
level of the land and sea 
must have been altered, 
laying bare a part of the 
smoothed sea bottom to 
form the coastal plain. 

As the region now 
stands higher than before, 
the rivers tend to wear 
down their valleys to the 
new level of the sea at 
their mouths; the valley 
sides waste away, and 
thus the valleys slowly 
become wider; but the 
streams cannot wear the valleys deeper than the surface 
of the sea at their mouths. The level of the sea is there- 
fore called the haselevel of the region. 

Slender belts of a very narrow coastal plain, less than a 
mile wide, are found along parts of the western coast of Scot- 
land; they are even narrower than the plain represented 
in Figure 62, being wide enough for only a single row of 




Fig. ()3. Sample Map of a Narrow 
Coastal Plain 



146 



ELEMENTARY PHYSICAL GEOGRAPHY 



fields. The houses of the farmers are generally placed 
near the inner margin of the plain; a few fields are cleared 
on the lower slopes of the back country; cattle pasture 
on the higher hillsides ; the cultivated crops are gathered 
chiefly from the smooth surface of the little plain. 




Fig. (Ji. A Narrow Coastal Plaiu in Scotland 

A number of narrow and low coastal plains occur along 
the coast of Oregon. They are one or two miles wide and 
twenty or more miles long. Heavily forested mountains 
rise in the background, too uneven for easy occupation; 
but the even surface and gentle slope of the coastal plains 
make them attractive to settlement, although they suffer 
the disadvantage of having no good harbors. 

The eastern coast of Mexico in the neighborhood of Vera 
Cruz is bordered by a low coastal plain about fifty miles 



PLAINS AND PLATEAUS 147 

wide, back of which the mountains rise rather abruptly. 
The plain is called the tierra caliente, or hot country. 
It is sandy, malarial, and relatively infertile. Vera Cruz, 
the chief port for the interior highlands, has a poorly 
protected anchorage on the open shore. 

98. Broad Coastal Plains. — Figure 65 represents a 
broader coastal plain than the precediag examples. The 




Fig. 65. Broad Coastal Plain 

outer part of this plain is much like the plain in Figure 62 ; 
but the inner part is more cut by branching valleys and 
ravines, so that it presents a hilly rather than a plain sur- 
face, and the larger rivers have broader valleys than before. 
The unevenness, . or " relief," of the surface increases 
inward from the shore line in consequence of the greater 
depth to which the valleys are cut in the higher part of 
the plain. "Where the uplands are much interrupted by 
branching valleys the plain is said to be well dissected. 



148 



ELEMENTARY PHYSICAL GEOGRAPHY 



During the slow uplift of the region different kinds of 
sediments may have been laid down near the shore, as the 
sea retired from the plain. Hence the soils of such plains 
are commonly of different kinds in the inner, middle, and 
outer parts, being arranged in belts roughly parallel to the 
length of the plain. 

The Atlantic coastal plain of the Southern States, of 
which a characteristic portion is included in South Caro- 
lina, Figure 66, 
is dissected by 
many branch- 
ing valleys in 
its inner part. 
It may be 
divided into 
several belts 
parallel to the 
shore line. 
The outer or 
coastal lowland 
is a smooth 
plain, with open 
pine woods or grassy savannahs ; this division is about fifty 
miles wide, rising so gently that it seems level to the eye. 
Its surface is very poorly drained. 

The plain slowly rises inland with gently rolling sur- 
face; here the soil is better than in the first belt, and much 
cotton is raised. Farther inland still the surface becomes 
more sandy again and more hilly, giving extensive views 
seaward across the lower plain. A hundred miles inland 




Fig. 66. Coastal Plain of the Carolinas 



PLAINS AND PLATEAUS 



149 



a belt of hilly uplands stands 600 or 700 feet above the 
sea, covered with pine forests. Here the plain is well dis- 
sected, its original surface being almost entirely destroyed 
by the action of many streams in carving their valleys and 
by the action of the weather in opening the valley slopes. 
Then come the hills of the older land (the Piedmont 
belt, here not momitainous, but of moderate relief), whence 




Fig. 67. A Truck Farm on the North Carolina Coastal Plain 



the strata of the plain have received their sediments, and 
where the rivers are now cutting dow^l narrow valleys 
beneath their former valley floors. 

The soil belts on this plain exert an important control over 
the industries of the people. The less sandy soils are occu- 
pied by cotton plantations. Extensive pine forests on the 
more sandy belts furnish much lumber, tar, and turpentine. 



150 



ELEMENTARY PHYSICAL GEOGRAPHY 



The moist swampy soils near the coast are well adapted 
to the cultivation of rice. The more limy layers of the 
plain are dug up to fertilize the more sandy fields, and the 
richest of these limy deposits are exported to other states 
to be used as fertilizers. In North Carolina numerous 
farms on the coastal plain furnish vegetables for the mar- 
kets of northern cities. 



99. Belted Coastal Plains. — Figure 68 exhibits a coastal 
plain which may be divided into three belts parallel to the 




Fig. 68. A Belted Coastal Plain 

shore line, each one ten, twenty, or more miles wide ; the 
innermost (A) is a lowland ; the middle belt (B) is an 
upland of stronger rock layers, several hundred feet above 
the lowland ; the outer belt (C) is a smooth coastal low- 
land. The several belts recall the beltlike arrangement of 
soils described in the case of a broad coastal plain, but 
here the middle belt forms an upland that runs about 



PLAINS AND PLATEAUS 



151 



parallel to the shore line and stands between an inner 
and an outer lowland. The upland descends by a rather 
steep slope to the inner lowland, and by a long, gentle, 
outlooking slope to the coastal lowland.^ 

In Figure 68 the front 
of the diagram is drawn 
to represent what would 
be seen on the side of a 
very deep cut that might 
be imagined to cross the 
plain. The layers of 
clays, sandstones, and 
other strata that form 
the plain are thus shown, 
gently slanting under the 
sea. Where is the upper- 
most layer of the series, 
that is, the layer that was 
last deposited ? What 
part of the belted plain 
does it cover ? Where are 
the under layers (the first 
deposited) ? "Where do 
they reach the present 
surface of the belted 
plain ? Which layers 
reach the surface of the upland^ part of the belted plain ? 

Draw an outline map of the district shown in Figure 68. A 
sample of part of it is shown in Figure 69. Note that some small 
streams must run inland, down the inner slope of the uj^land. 




Fig. 69. 



Sample Map of Part of a Belted 
Coastal Plain 



1 An upland of this kind may be called a cuesta, following a word of 
Spanish origin used in New Mexico for low ridges of steep descent on one 
side and gentle slope on the other. 



152 ELEMENTARY PHYSICAL GEOGRAPHY 

Compare the arrangement of the rivers and streams with those 
shown in the map, Figm-e 63, di-awn from Figure 62. 

The reason for the arrangement of upland and lowland 
may now be understood. The under layers of this coastal 
plain are weaker than the middle layers ; hence the under 
layers, which reach the surface of the plain near its inner 
border, are already worn down to a lowland, while the more 
resistant middle layers still preserve an upland height. 

Trace the river first seen at D, Figure 68, and describe the several 
belts of country that it crosses on the way to the sea. Where is its 
valley deep ? where shallow ? 

A good example of this kind of coastal plain is found 
in southern New Jersey, Figure 70. The Delaware river 
below Trenton runs along the inner lowland. Here is a 
belt of pottery clays, of which much crockery and earthen- 
ware are made. Then comes a belt of farming country 
on rolling hilly ground, which contains laj^ers of marl 
(limy clay); the marl is dug to serve as a fertilizer on less 
productive soils. The hills rise to an upland that descends 
in a long gentle slope southeastward to a lowland plain 
by the sea ; its soil is sandy and its even surface is gen- 
erally overgrown with pine forests. Short arms of the 
sea enter the lower valleys, giving harborage for small 
vessels ; many fishermen live in the shore villages. A 
belt of shallow salt>-water lagoons with extensive marshes 
of reeds borders the mainland for a breadth of about five 
miles. Finally come the sand reefs, half a mile or more 
wide, inclosing the lagoons. The reefs are interrupted by 
inlets, connecting the lagoons with the sea. 



PLAINS AND PLATEAUS 



153 



Name the direction of the Delaware and the Schuylkill as they 
flow into the inner lowland ; of the Delaware in the inner lowland ; 
of the streams that flow down the inner slope of the cuesta and 




5 10 15 20 



Fig. 70. The Belted Coastal FlMn of Southern New Jersey 



across the marl belt ; of the streams on the outer slope of the 
cuesta. Which is the steeper slope of the cuesta? How is this 
known ? Compare the arrangement of all these streams with those 
shown in Figure 08. 

What is the average breadth of the clay belt ? of the marl belt ? 
of the hilly belt? of the sandy plains? of the coastal lowland? 
How far is it from Philadelphia to Atlantic City? 



154 ELEMENTARY PHYSICAL GEOGRAPHY 

100. Embayed Coastal Plains. — The region here figured 
does not at first sight seem to belong to the family of 
coastal plains. Long shallow arms of the sea enter 
between low hilly arms of the land. Rivers from the 
back country enter the heads of the long bays ; small 
streams from every little valley between the hills of the 




Fig. 71. An Embayed Coastal Plain 

land arms enter little bays or coves on the sides of the 
larger bays. 

This diagram represents a coastal plain which has been 
depressed, so that its valley floors are " drowned " beneath 
the sea. Before drowning, the region must have stood 
for a long time higher above baselevel than now, for the 
valleys evidently had been eroded and widely opened before 
the depression of the region occurred. Many side valleys 
had been formed, so that the uplands between the larger 
rivers had been dissected into branching spurs. Now the 
outer coastal lowland and the broad valley floors are under 



PLAINS AND PLATEAUS 



155 



water, the latter being occupied by the bays that enter far 
toward the oldland, while the groups of hills stand forth 
as ragged arms of the land. The former simple shore Hne 
is thus exchanged for a very 
irregular shore line. 

Draw a map of part of the em- 
bayed coastal plain shown in Fig- 
ure 71, after the style of the outline 
in Figure 72. Compare Figures 65 
and 71. Point out the inner border 
of the coastal plain in each one. In 
what respects do the two figures 
agree? In what do they differ? 
How has the difference been pro- 
duced? In each one trace a river 
from the oldland to its mouth. 
What difference is noted? 

The relative change in the 
attitude of land and sea is here 
opposite to that inferred in the 
previous examples. Since 
the depression of the region the 
land heads have been more or 
less cut back by the waves, and 
the bay heads have been some- 
what filled by marshy deltas. But the drowning cannot 
have taken place long ago, as the earth counts time, for 
the changes in the land heads and bay heads are of 
moderate amount. 

The Atlantic coastal plain from Delaware bay to Pamlico 
sound presents many examples that fall under this class. 




Fig. 72. Sample Map of an Em- 
bayed Coastal Plain 



156 ELEMENTARY PHYSICAL GEOGRAPHY 

The outer shore line is for the most part a sand reef, 
inclosing lagoons. Many branching bays extend inland, 
the largest being Chesapeake bay. Navigable arms of 
the sea thus alternate with dissected arms of the land. 

Partly drowned coastal plains exert a peculiar control 
over the distribution and occupation of their population. 
The greater part of the valley lowlands is lost, and the 
people must make the most of the hilly land arms that 
remain above sea level. The axis of each of the larger 
arms is generally followed by a main road, making its way 
from village to village among the upland farms and giv- 
ing forth side roads to villages on the smaller land arms 
or at the little bay heads. Indicate the place of such 
roads and villages on Figures 71 and 72. 

The shallow bays are valuable for fishing grounds. 
More important centers of population are found either 
near the heads of the larger bays, where the large rivers 
come out from the back country and reach tide water, or 
near the mouths of the bays where the outer sand reefs 
are not continuous and the ocean is easily reached. 
Baltimore and Norfolk are good examples of cities thus 
situated. The outer shore line is inhospitable; its long 
sand reefs offer no good landing place, and the narrow 
tidal inlets allow entrance only to small-sized vessels. 
Where would such a view as that of Figure 73 be found 
in Figure 71 ? 

In the early history of "tide-water Virginia" the 
numerous drowned valleys afforded easier communication 
between the settlements than was found overland through 
the forests of the coastal plain. 



PLAINS AND PLATEAUS 



157 



101. The Fall Line. — A large river whose valley is 
extended across a coastal plain often lias low falls or 
rapids near the inner margin of the plain, which determme 
the " head of navigation," or uppermost point that can be 
reached by vessels from the river mouth. A Ime drawn 
tlrrough the falls on successive rivers is called the fall line. 




Fig. 73. A Brauch oJ: Chesapeake Bay, Maryland 

The falls occur where the river passes from a steeper slope 
on the resistant rocks of the older land to a nearly level 
channel excavated in the weak strata of the plain. 

On coastal plains of a considerable breadth settlements 
near the mouth and at the head of navigation of the larger 
rivers often develop into important cities. The lower 
city is the seaport of the region. The upper city bears 
closer relation to local industries and traffic; it hes in 
the midst of a diversified region, with strong water power 
for manufacturing the varied products of rock and soil. 
In South Carolina, Columbia lies on the Congaree river, 



158 ELEMENTARY PHYSICAL (GEOGRAPHY 

where it passes from the older land to the dissected plain. 
Charleston lies at the outer edge of the coastal lowland 
on the widened course of a small river where the tide 
comes in from the sea. 

The fall line along the inner margin of the Atlantic coastal 
plain of the United States is marked by important cities on 
nearly every large river that crosses it. Trenton, Philadel- 
phia (at the falls of the Schuylkill), Richmond, Raleigh, 
Camden, Columbia, and Augusta are all thus located. 

The origin of the forces sufficient to deform the crust 
of the earth and to elevate or depress a coastal plain is not 
well understood. It is necessary that the student of 
physical geography should recognize that elevation and 
depression have actually taken place, and should under- 
stand the importance ' of such movements in controlling 
the forms of the lands and the conditions of their inhab- 
itants ; but the processes that cause such movements must 
be left to the more advanced study of geology. 

Coastal plains, narrow or broad., belted or embayed, occur 
along parts of the border of different continents. They 
resemble more or less closely the examples here given. 
The coastal slope of Guiana and the plains of Patagonia, 
South America, belong in this group of forms. 

102. Inland Plains. — The Great plains of the central 
United States slope gently forward from the Rocky moun- 
tains. They are formed of many layers of sands, clays, 
and gravels, washed from the mountains and now lying 
one over the other, many hundred feet in total thickness 
and nearly horizontal. Some of the layers were deposited 



PLAINS AND PLATEAUS 159 

when the region was below sea level ; some were spread 
over the uplifted sea bottom by rivers when the region was 
too low to be dissected. 

The plains are now high enough to be more or less 
dissected by streams and rivers whose valleys vary in 
depth and width ; but the upland spaces between the val- 
leys often preserve a comparatively even surface over 
large distances. In some districts, vast areas stretching 
farther than the eye can reach are monotonously even 
and almost as uniform in soil as in surface. In other dis- 
tricts, valleys are deeper and closer together, and the 
spaces between them are made hilly by the branching 
ravines of side streams. 

Within the United States the Great plains are treeless 
for 500 miles east of the Rocky mountains, except on 
certain hills and bluffs which occasionally rise above 
the general level, or in the valleys which sink below 
it. The absence of trees is due to the dryness of the 
climate, and this in turn is due to the general course of 
the westerly winds whose moisture has been left on 
the mountain ranges between the plains and the Pacific. 
Agriculture is impossible in the drier southern parts 
without irrigation. Farther north in Canada the climate 
is moister, and the plains are forested. In still higher 
latitudes the surface is treeless; the warmth of summer 
melts only the upper part of the soil, and vegetation is low 
and stunted. 

The treeless plains possess little mineral wealth, and they 
have no forests to supply lumber; hence they cannot 
become a closely populated manufacturing region ; but they 



160 ELEMENTARY PHYSICAL GEOGRAPHY 

have a more or less abundant growth of herbage, which 
once supported herds of countless buffaloes. Now that 
the buffaloes have been killed off, their place is taken by 
cattle which range over the plains, wandering back and 
forth over the uplands between the valleys that they visit 
for water. A number of railroads traverse the plains and 
carry, among other things, many cattle to eastern markets. 

The plains of western Siberia resemble the Great plains 
of the central United States. They slope gently away 
from the mountains of central Asia. They have a mod- 
erate altitude above sea level and preserve a generally 
even surface over hundreds of miles. Marshes and shal- 
low lakes lie in faint depressions, as if the hollows in the 
original surface of the plains had not yet been drained by 
river action. The narrow valleys are few and far between ; 
they can never be cut deep while the region stands low, 
and they have not yet been worn wide. 

The more northern part of these plains is treeless because 
the ground is frozen. The central part is forested; but 
south of latitude 50° to 55° the plains have a light rainfall 
and are again treeless ; clothed with thin grass in summer ; 
cold, barren, and wind swept in winter. 

The treeless plains have long been the home of wander- 
ing tribes, whose wealth is not in fixed possessions, but in 
herds and flocks driven from place to place for pasture. 
The people live in tents and move about without definite 
limits to their lands. On account of their wandering 
habits they are called nomads (wanderers). Every man 
is necessarily a horseman, skilled in nearly all the arts of a 
wandering life. 



PLAINS AND PLATEAUS 



161 



103. Belted Inland Plains. — In Wisconsin, far inland 
from the ocean, the northern part of the state is occupied 
by rugged highlands of resistant rocks. Adjoining on the 
south and east are plains and uplands arranged in belts, 
their rock layers sloping gently away from the highlands 
and lapping one 
over another like 
great shingles. 

Fragments of the 
highland rocks are 
found in the lower 
members of the over- 
lapping strata; nu- 
merous marine fossils, 
like corals and shell- 
fish, occur in many 
layers. All the lay- 
ers are well consoli- 
dated ; the firmer 
ones form belts of 
hilly uplands, between which the weaker layers are worn 
down to lower plains. 

Although the sea may now be a thousand miles away, 
the belts of upland and plain are easily seen to be similar 
to the belted coastal plains already described, while the 
rugged highlands are the older land from which the strata 
of the plains and uplands were long ago derived. 

This is an ancient coastal plain ; that is, a region that 
began its existence as a coastal plain ages ago in the 
earth's history, and that now stands in the interior of the 




Fig. 74. Ancient Coastal Plain of Wisconsin 



162 ELEMENTARY PHYSICAL GEOGRAPHY . 

continent because successive uplifts have broadened the 
continental surface. 

Belted inland plains, similar to the example in Wiscon- 
sin, occur in many parts of the world, usually presenting 
a succession of hilly uplands and intermediate plains sim- 
ilar to those here described. Good examples are found 
in south-central England and in northeastern France. 
They all enjoy the advantage that comes from diversity of 
form and products and from the resulting variety of occu- 
pations that they support. 

104. Plateaus. — When plains stand at a considerable 
height above the sea level they are called plateaus. No defi- 
nite limit of height can be given to separate the two classes 
of forms. In elevated regions the lower parts may be called 
plains, even though they are more than 2000 or 3000 feet 
above sea level; in low regions the higher parts may be called 
plateaus, even though not higher than 1000 or 2000 feet. 

Plateaus are sometimes traversed by deep and narrow 
valleys or canyons, branching in various directions. The 
canyons are cut down to a great depth by their streams 
because the plateau surface stands high above baselevel. 

Plateaus are generally built of horizontal rock layers of 
various kinds, whose edges are well shown in the canyon 
walls. In Figures 75, 76, and 77 a deep cut is imagined 
across the front of the view, so as to show more clearly the 
rock layers that crop out in the canyon walls. The broad 
uplands between the canyons have a comparatively even 
surface across which it is easy to travel, but the deep 
canyons are almost impassable. 



PLAINS AND PLATEAUS 



163 



The walls of the narrower canyons consist of a succession 
of cliffs and slopes, often too steep to be climbed. The cliffs 
are formed on the hard resistant layers, which are strong 
enough to stand with a steep face ; the slopes are formed on the 
weak layers, which are more easily weathered back to a slant. 




The slopes are covered with coarse 
rock waste, or talus, weathered from 
the cliffs above. The rock waste weathers and falls from 
each cliff, and rolls, washes, and creeps down each slope to 
the top of the cliff next below, where it falls again, shatter- 
ing to fragments ; at last it reaches the stream, where its 
finer parts are rapidly washed away. Thus the chffs and 
slopes wear back or retreat, and the canyon widens. 

As a canyon widens, a platform or bench is formed on 
the top of the stronger cliffs ; it is then often possible to 
descend into the canyon by climbing down crevices in the 
cliffs, from platform to platform. 



164 



ELEMENTARY PHYSICAL GEOGRAPHY 



Point out the cliffs, slopes, and platforms of the canyon walls in 
Figures 76 and 77. Where are the highest cliffs, the longest slopes, 
the broadest platforms? Which layers, shown in the front of the 
diagram, are resistant ? Which are weak ? 

The slow creeping of waste down the slopes of the valley 
sides is caused by very slight movements of the fragments 
and particles as they warm by day and cool by night, as 




Fig. 76. Diagram of a Narrow Canyon 

they are wet by rain and dried in fair weather, or as they 
are moved by the freezing and thawing of films of water 
between them. The movement is more noticeable on steep 
slopes, but it does not cease even on the gentler slopes. 

The slow downhill creeping of weathered fragments, 
aided by the surface washing of fine particles in wet 
weather, is the chief means of moving waste down from 
the liigh ground to the streams in the valley bottoms. 

As the canyon is eroded by the main river, ravines are cut 
in the canyon walls by streams that rise on the plateau, 



PLAINS AND PLATEAUS 



165 



The deeper the main canyon is eroded, the deeper the 
side ravines are worn down, and the more the plateau is 
dissected. Yet in the stage shown in Figure 77 the great 
work of wearing away the plateau is only well begun. 

The lofty plateaus of northern Arizona are traversed from 
east to west by the Grand canyon of the Colorado, from 
4000 to 5000 feet deep. The dry climate of the plateau 







Fig. 77. Diagram of a Widened Canyon 

makes vegetation scanty. The region offers no temptation 
to settlement, however marvelous it is to the explorer. 
Much of it is desolate, occupied by a few Indians, who 
subsist by "cultivating little patches of corn, gathering 
seeds, eating the fruits and fleshy stalks of cactus plants, 
and catching a rabbit or lizard now and then; dirty, 
squalid, but happy, and boasting of their rocky land as 
the very Eden of the earth." 

The great elevation of this plateau pennits an unusual 
depth of canyon cutting. The massive strong and weak 



166 ELEMENTARY PHYSICAL GEOGRAPHY 

strata of which the plateau is built produce strong cliffs 
and long talus slopes on the canyon walls. Far down in 
the bottom of the great trench runs the tawny Colorado, 
turbid with waste that is showered from the walls in rocky 
avalanches or swept in from side canyons by cloud-burst 
torrents. The water, bearing abundant waste, is stiU rasp- 
ing down the rocks in its falls and rapids. Deep as the 
canyon is, it has been cut down only by the river. There 
is no indication of clefts or fractures along the river course. 

Unlike most great rivers whose valleys serve as paths of 
travel, the Colorado is almost inaccessible along its canyon. 
Only one exploring party has successfully gone down the 
canyon, and their narrative is a wonderful history of scien- 
tific adventure. When their boats once entered the canyon, 
retreat was impossible against the swift current. Escape 
by climbing the walls was hazardous. To descend the river 
was easy on its smooth stretches, even though hemmed in by 
great chff s ; but cascades plunge over ledges where the most 
resistant rock layers are not yet cut through, and rocky 
rapids obstruct the channel where side canyons dehver 
heaps of bowlders to the main river. After many perils 
the party came out to the open lower country on the west. 

Plateaus interrupted by narrow canyons are, as a rule, 
occupied only on their upland surface. The elevation of 
the upland is an advantage in the torrid zone, where the 
high temperatures at sea level are wilhngly exchanged by 
civilized races for a more moderate temperature at altitudes 
of several thousand feet. But in the temperate zone a 
high plateau is at a disadvantage from the rigor of its 
winters, as well as from its difficulty of access. 



PLAINS AND PLATEAUS 167 

The canyonlike valleys are obstacles to movement ; they 
serve as barriers (except to birds and winged seeds) between 
the uplands on each side. They are seldom inhabited, 
unless by the people of a persecuted tribe, who sometimes 
take refuge as "cliff dwellers" in the recesses or caves 
that are often excavated between cliff base and talus top. 

105. Dissected Plateaus The rugged uplands that 

extend continuously from New York to Alabama, known 
as the Catskill, Allegheny, and Cumberland plateaus, may 
here be treated together under the second name. The 
whole region is occupied by mountainlike hills and spurs, 
built of nearly horizontal rock layers and separated by , 
numberless deep valleys that have been eroded by the riv- 
ers and their branching streams. The hilltop view gen- 
erally discloses a rather even sky hne, which may be taken 
to mark a plateau surface that once extended over the 
whole region, before the branching valleys were carved. 

The Allegheny plateau is now thoroughly dissected by 
its streams. It is evidently in a more advanced stage of 
change than a plateau that has only a few narrow canyons. 
The altitude of the original upland in West Virginia 
(roughly 2500 or 3500 feet) has been great enough to per- 
mit the erosion of valleys 1000 feet or more in depth; 
hence some of the plateau remnants fairly deserve the 
popular name of " mountains," locally applied to them. 

Many resistant sandstone layers stand out in chffs from 
ten to fifty feet high. As the layers are nearly horizontal, 
the cliffs run in bands around the spurs of the great 
hills, but are usually liidden by the heavy forest that 



168 



ELEMENTARY PHYSICAL GEOGRAPHY 



covers much of this region. The weak strata occupy the 
intervening slopes, covered with a thin stony soil and sup- 
porting forest trees. The hills and spurs are all very 
much alike, for they have been 



dissected by similar streams 
Every side valley resem- 
bles its neighbors; / -s'^ 
all the members ^^ 
of a local tribe 
of small 

streams / ^ Xtt . i n „ \ ••..m^-s/ ri A' ^cascade 

down over 

the same 

v^' J^}sn^ X-^number of f all- 

^/,\/Jx making strata in 

their descent to the 

-^,V larger rivers. 

In contrast to the previous 

example, this district has nearly 

everywhere lost its once continuous 

upland surface and is now transformed 

into a well-dissected hill-and-valley country. 

A great part of the surface consists of hillside 

slopes. Drainage is not delayed on extensive 

uplands ; but at times of rain or winter thaws 

water is quickly shed from the hills, and the 

main streams rise rapidly in destructive floods. 

The forests retard but do not prevent the wash of waste 

from the steep slopes ; a great load of waste is delivered by 

the side streams to the rivers. 




Fig. 78 

The Allegheny 

Plateau 



PLAINS AND PLATEAUS 169 

What parts of what states are occupied by the Allegheny plateau ? 
Which state has the greatest part of its area in the plateau ? What 
cities can you name in that state ? How far is it from the Catskill 
mountain district to the Cumberland plateau district ? 

As a whole, the Allegheny plateau is so rugged that its 
population is small, being generally found on isolated farms 




Fig. 79. Canyon of Kaftawlia River in Allegheny Plateau, West Virginia 

upon the disconnected uplands, in villages and occasional 
small cities in the valleys, or gathered about mines or 
other industrial works. The isolated hilltop farmers can- 
not afford to construct and maintain good hillside roads ; 
it is difficult to haul upland products down bad roads to 
village markets or to railroad stations, and it is doubly 
difficult to haul supplies up .to the farms. Life on the 
uplands is laborious. 

The hillsides are generally too steep for cultivation ; if 
cleared, the soil is rapidly washed away. Wild animals, 



170 ELEMENTARY PHYSICAL GEOGRAPHY 

such as deer and bear, almost exterminated from the lower 
country on the east and west, still find refuge here ; small 
game is abundant, and hunting is almost as much of an 
occupation to the " mountaineers " as farming. 

The forests supply lumber to the more thickly settled 
communities on the east and west. The numerous coal 
seams (vegetable deposits in ancient marshes, now members 
of the great series of horizontal strata that build the 
plateau) are well exposed on the sides of the deep-cut 
valleys, and are now extensively mined. Iron ore occurs 
in certain strata. Rock oil and natural gas are found by 
boring deep wells. It is chiefly in comiection with the 
industries dependent on these important products that a 
larger population is to-day attracted to this rough country; 
In the earlier history of the United States the dissected 
Allegheny plateau was (excepting the North Carolina 
mountains) the most formidable barrier between the Atlan- 
tic coastal plain and the open prairies of the Ohio valley. 

Intercourse and traffic are still so difficult in the districts 
of stronger relief, away from the lines of travel, that the 
people of the Allegheny plateau are slow in acquiring the 
ways of civilization. Family feuds are still maintained 
among the " mountaineers " of West Virginia and Ken- 
tucky. As the uplands decrease in height westward, and 
the valleys become more open toward the Ohio river, popu- 
lation increases ; but Pittsburg is a city of exceptional size 
in this region. Its growth, in early years was favored by 
its position with reference to the lower Ohio valley, and in 
later years by the great stores of mineral wealth in the 
surrounding country. 



PLAINS AND PLATEAUS 171 

106. Mesas. — Broad plains of gently rolling surface, 
drained by streams in wide-open, flat-floored valleys, are 
sometimes overlooked by flat-topped " table mountains " 
of horizontal rock layers. Neighboring tables are of nearly 
uniform height, each one being capped by the same kind 
of cliff-making rock layers and flanked by a sloping talus. 
In the western United States tables of moderate height are 
often given the Spanish name mesa (table ; pron. may-sa) ; 
while the smaller mesas are known by. the French name 
hutte (target or landmark; pron. hewt). 

Mesas and buttes of this kind are all that now remain 
of a plateau that once spread far and wide over the region. 
The open space between the mesas has been produced 
by the widening of the valleys, so that their floors now 
occupy a great part of the surface. The original level of 
the plateau may have been much higher than the tops of 
the mesas, for the uppermost strata may now be com- 
pletely washed away. A region of this kind represents an 
approach to what may be called the old age of a plateau, 
when even the mesas will be worn away, leaving an 
unbroken plain. It is very unlike the youth of the plateau, 
when the uplands were broad plains and the valleys were 
narrow canyons. 

The plains of western New Mexico are surmounted by 
numerous mesas or plateau remnants. Settlement here is 
chiefly limited to the lower lands. The isolated mesas and 
buttes, rising several hundred feet above the plains, are 
generally uninhabited. 

The mesas of an old plateau are not, like the canyons of 
a young plateau, serious obstacles to travel ; for while 



172 ELEMENTARY PHYSICAL GEOGRAPHY 

canyons continue for long distances and are everywhere 
difficult to cross, mesas are generally of moderate length, 
and many broad passages are opened among them. They 
are occasionally occupied as natural citadels by barbarous 
tribes. 

One of the most remarkable remnants of an old plateau 
is the so-called Enchanted mesa of western New Mexico. 




Fig. 80. The Enchanted Mesa, New Mexico 

It rises more than 400 feet above the surrounding plain, 
and although no longer inhabited, it was once occupied by 
a small tribe of Indians, who found safety on its almost 
inaccessible summit. 

Other mesas in New Mexico and Arizona are still 
occupied by Indians, whose compact groups of houses on 
the upland cannot, at a little distance, be distinguished 
from the rock walls of the cliffs. The Indians cultivate 
small patches of corn on the lower ground, but they have 
not ventured to build villages there for fear of attack from 
more warlike tribes. 



PLAINS AND PLATEAUS 



173 



In the interior of British Guiana gigantic remnants of an 
old plateau rise above the surrounding lower country. .Huge 
mesas are rimmed round' by almost inaccessible cliffs that 
stand above long talus slopes. One of the highest is Roraima, 
whose broad table is more than 2000 feet above its base. It 
is uninhabited, and until recently had never been ascended. 




Fig. 81. Broken Plateaus 



107. Broken Plateaus. — The plateaus of northern Ari- 
zona, of which the Sheavwits already described is one, 
stand in a curious relation to one another. East of the 
Sheavwits comes the Uinkaret, presenting the same upland 
(diversified by volcanic cones and lava flows), and expos- 
ing the same succession of cliffs and talus slopes in the 
canyon walls; but the Uinkaret stands about 1800 feet 
higher than the Sheavwits. The two are separated by a 
high and ragged cliff, or escarpment (CA, Figure 81), 
known as Hurricane ledge, facing westward. 



174 



ELEMENTARY PHYSICAL GEOGRAPHY 



The section exposed in the canyon (A, Figure 81) 
shows that the cliff stands on the line of a great north- 
and-south fracture, which divides the whole mass of 
strata into two blocks, the eastern block (Uinkaret) 
being lifted nearly 2000 feet higher than the western 
(Sheavwits). Several other similar plateau blocks are 
found in this region. The displacement of the blocks is 




Fig. 82. Hurricane Ledge, a Dissected Fault Cliff 



clearly represented in the section on the right front of the 
diagram, Figure 81, under the letters B, B, E. 

The western boundary of the Sheavwits plateau {FD, 
Figure 81) is one of these cliffs of displacement, 2000 or 
3000 feet high. It is cut by gigantic ravines, from which 
great volumes of rock waste are washed out. 

Fractures of this kind, on which adjacent blocks of land 
are displaced, are called faults. The cliffs that originate 
on the broken face of the uplifted blocks are called fault 
cliffs. They are in time more or less worn back by 



PLAINS AND PLATEAUS 175 

\ weathering and by the growth of ravines, such being the 
present stage of Hurricane ledge ; and they may then 
be called dissected fault cliffs. 

The forces by which the plateau blocks have been 
broken and lifted have not been fully explained. It is 
probable that violent earthquakes accompanied the produc- 
tion of the fractures, and that the displacement of the 
blocks was accomplished by many small movements, each 
causing a moderate earthquake. 

QUESTIONS 

Sec. 96. Describe the natural processes in operation on a moun- 
tainous district bordering the sea. Consider the relation of such a 
district to habitation. Give an example. 

97. Describe a narrow coastal plain. Describe its valleys and 
their lateral ravines. Explain their origin. What can be inferred 
as to the future form of such a plain ? as to its past form ? How 
can the origin of such a plain be accounted for? Define baselevel, 
and state the relation of rivers and valleys to baselevel. Describe 
a narrow coastal plain in Scotland ; in Oregon ; in Mexico. 

98. Describe a broad coastal plain. What is meant by relief? 
Describe the coastal plain of the South Atlantic States as to form ; 
as to soil ; as to industries. Why are its soils arranged in belts ? 
Compare it with the narrow coastal plain of Scotland. What 
products are derived from it? 

99. Describe a belted coastal plain. What is the origin of its 
form ? What is a cuesta ? Describe the course of the streams with 
respect to a cuesta. Describe the belted coastal plain of New Jersey. 

100. Describe an embayed coastal plain as to hills, valleys, and 
bays. Explain its origin. How has the depression of the region 
affected the form of the coast line? Describe an example of this 
class. Describe its effects on the distribution and occupation of its 
population ; on the location of roads, villages, and cities. 



176 ELEMENTARY PHYSICAL GEOGRAPHY 

101. Where may falls be expected in rivers that cross coastal 
plains? What is the cause of the falls? What is the fall line? 
Where are cities likely to be situated on the rivers of coastal plains? 
What cities lie on the fall line of the Atlantic coastal plain? 

102. Describe the Great plains of the central United States as to 
origin, form, climate, vegetation, and industries. Describe the 
extension of these plains into Canada as to climate and vegetation. 
Describe the plains of western Siberia as to form, climate, and popii- 
lation. Why are the valleys in these plains shallow? What is 
the relation between nomads and inland plains? 

103. What is a belted inland plain ? Describe an example from 
Wisconsin. Explain its origin. Where may some other inland 
belted plains be found? 

104. Compai-e plains and plateaus. Describe a canyon as to 
form and origin. Compare the form of the canyon walls as shown 
in the diagrams of a narrow and a widened canyon. Explain their 
differences. What is the relation of strong and weak rock layers to 
form ? Describe the movement of rock waste in a canyon. Describe 
the plateaus of northern Arizona. Describe the Colorado river and 
its canyon. Why is it difficult to follow the river? What is the 
value of plateaus to habitation? of canyons as barriers? 

105. What is a dissected plateau? Describe the Allegheny plateau 
as to location, extent, altitude, and form. Describe the hillsides; 
the streams ; the drainage ; the industries ; the products of this 
plateau. What is the condition of its people? 

106. Describe mesas and their surroundings. How are mesas 
formed? Compare a mesa and a canyon. Compare the plateaus of 
northern Arizona, the dissected Allegheny plateau, and the mesa 
district of New Mexico. Describe the Enchanted mesa ; Roraima. 

107. What is meant bj^ broken plateaus? Describe the broken 
plateaus of northern Arizona. How are they separated? What is a 
fault? a fault cliff? a dissected fault cliff'? What is the relation of 
earthquakes to broken plateaus ? 



CHAPTER VI 
MOUNTAINS 

108. Mountain Ranges. — The peaks and ridges of moun- 
tains are generally grouped in belts of much greater length 
than breadth, called mountain ranges. When several ranges 
are grouped together they constitute a mountain chain. 
Unlike plains and plateaus, in which, as has been stated in 
the preceding chapter, the rock layers are nearly horizontal, 
mountain ranges are belts of disordered structure in the 
earth's crust. Sometimes the strata are broken, displaced, 
and tilted as if gradually disturbed by some great uplifting 
force from beneath; sometimes the strata are bent and 
folded, as if slowly compressed by some irresistible crush- 
ing force from one side. 

The origin of the forces which produce mountains is 
not fully understood. One of the most ingenious and 
satisfactory theories accounts for many ranges as great 
disorderly folds formed in the crust of the earth, which 
is thoughi: to wrinkle here and there as it very grad- 
ually settles down on the slowly cooling and contracting 
interior. 

Streams carve deep valleys in the uneven surface pro- 
duced by mountain upheaval. Mountains as we see them 
are therefore the result of deforming forces which slowly 

177 



178 



ELEMENTARY PHYSICAL GEOGRAPHY 



raise the mountain belt to great height, and of eroding 
forces which still more slowly wear down the uplifted belt 
by carving valleys in it. 




Fig. 83. A Mountain Peak 



109. Block Mountains. — In southern Oregon and the 
adjoining parts of California and Nevada there are many 
long narrow mountain ridges, extending about north and 
south. Each ridge is a few miles wide, ten to forty miles 



MOUNTAINS 



179 



long, and 1000 or more feet high. The ridges are steep 
or cliff-like on one side, of gentler slope on the other, and 
are separated by flat trough-like depressions of varying 
breadth and depth. A general view of the country shows 
that the entire region was once a plain, but that it has been 
gradually broken into long narrow blocks, and that the 
blocks are tilted one way and the other, so that their 
uplifted edges form the mountain crests. 




Fig. 84. Block Mountains 



Which block mountain is completely shown in Figure 84 ? How 
does it end ? (Note : the space included in the figure is too small 
to show the whole length of most of the mountains ; the northern 
part of sonae and the southern part of others are cut off.) Describe 
a large block mountain ; its crest line, its cliff face, its back slope. 
Where could it be best ascended ? 

Some of the ridges still preserve the form of the tilted 
blocks, hardly changed by weathering ; their sloping backs 
are smooth; their cliff ed fronts have little talus at the 
*base. Others have shallow gullies worn down the back, 
while the cliffs are indented by ravines, and every ravine 
has a fanlike deposit of rock waste spread out beneath it; 



180 



ELEMENTARY PHYSICAL GEOGRAPHY 



between the fans the cliffs have a distinct talus slope at 
their base. Yet the mountain blocks of Oregon are, on 
the whole, so little worn that they must have been broken 
and tilted recently in the earth's history. 

Earthquakes are not infrequent in this region ; hence it 
is believed that the tilting of the blocks is still in progress 
from time to time ; a movement of even a few inches would 
suffice to cause earth tremors, while a sudden start of a foot 

or more would produce 
a violent and destructive 
shock for many miles 
around, gradually fad- 
ing away at greater dis- 
tances. There is no sign 
that volcanic action has 
any connection with the 
fractures and earth- 
quakes of this region. 
The drainage of the 
block mountains is very 
simple, for the streams follow the slopes produced by the 
tilting of the blocks. The smaller wet-weather streams flow 
down the slopes of the ridges. Larger streams flow along 
the troughs in the direction of their slant to the deepest 
depressions, and there form shallow lakes and marshes. 
The finer waste from the ridges is spread evenly over the 
lower parts of the troughs, concealing their rocky floor. 

Certain features of the region depend on its arid climate. 
The rainfall is light (fifteen inches or less a year), for the 
Sierra Nevada and Cascade ranges on the west take niost 




Fig. 85. Mountains of Southern Oregon 



MOUNTAINS ' 181 

of the moisture from the Pacific winds. Few of the lakes 
are filled to overflowing ; they discharge their water supply 
by evaporation into the dry air. Most of the lakes are 
therefore saline, and the plains of fine waste about them 
are barren. 

In dry seasons the lakes shrink ; some of them disappear, 
leaving smooth floors of sun-baked clay. The bottom of the 
troughs elsewhere and the lower slopes of the ridges are 
clothed with bunch grass and sagebrush ; the ridge slopes, 
receiving more rainfall than the lower lands, support 
scattered cedars, and the higher crests bear forests of pine 
and spruce. 

Although the ridges are of moderate height, they repel 
the few settlers in the region, whose ranches are all found 
in the troughs. The thin grass supports scattered herds 
of cattle, and the streams suffice for a little irrigation. 
Thus even in these low young ridges the effect of moun- 
tains on climate, distribution of vegetation, and location 
of settlements is well shown. 

110. Dissected Ranges. — In Nevada and the adjoining 
parts of California and Utah there are many north-and- 
south mountain ranges from twenty to eighty miles long, 
and from five to twenty miles wide. Their summits rise 
from 5000 to 7000 feet above the plains. Their crests 
are notched and uneven ; their slopes are varied by well- 
carved spurs between deep valleys. The troughs between 
the ranges contain long slopes of gravelly waste that have 
spread out from the valleys when the streams are flooded. 
As compared with the ridges of southern Oregon, these 



182 



ELEMENTARY PHYSICAL GEOGRAPHY 



ranges are larger and more dissected. They possess more 
of the beauty and variety of form generally found in 
mountains. 

The ranges of Nevada, like the ridges of Oregon, seem 
to have been formed by the uplifting of long blocks of the 
earth's crust: but in Nevada the blocks must have been 




Fig. 86. A Dissected Mountain Range, Utali 

larger and the uplifting greater; and the uplifting must 
have begun earlier than in Oregon, for the work of dis- 
section by streams is here much further advanced. The 
ranges of Nevada are thoroughly or maturely dissected. 
Yet, as in Oregon, occasional earthquakes show that the 
mountains are still growing. 

The higher ranges in Nevada exhibit more distinctly 
than the smaller ranges of Oregon the lower temperature. 



MOUNTAINS 183 

with greater cloudiness and rainfall, that prevails on the 
mountains as compared with the plains between them. 
The rainfall on the plains is light, but storm clouds 
often gather round the peaks while the sun shines else- 
where. When the clouds dissolve, the mountains have 
been refreshed by rain or whitened with snow, while the 
plains may be as dry as before, except where the turbid 
flooded streams rush out from the mountain valleys. The 
streams generally wither away on the gravelly plains. 
Settlements in Nevada are therefore commonly limited to 
a belt around the mountain base, where the streams may 
irrigate fields. Some of the ranges contain valuable ores ; 
hence mining towns have sprung up in their valleys. 

111. Folded Mountains. — The Jura mountains, along 
the border of France and Switzerland, occupy a belt of 
country where the rock layers, once horizontal, have been 
slowly pressed into a series of wavelike folds. The moun- 
tains consist of a number of parallel ranges and valleys 
trending about northeast and southwest. Each range con- 
sists of a series of rock layers bent upward like an arch; 
each valley is underlaid by the same series of layers bent 
downward like a trough. Some of the uppermost layers 
have been weathered off from, the crest of the arches; 
the edges of the harder layers remain in flanking ridges. 
Waste from the arches has accumulated in the troughs, 
flooring them with gravel and sand. 

The rock layers of these mountains contain sea fossils ; 
the layers must originally have been horizontal strata on 
the floor of an ancient sea. Since then they have gradually 



184 



ELEMENTARY PHYSICAL GEOGRAPHY 



been pressed and folded into their arch-and-trough struc- 
ture by a powerful side pressure. 

The drainage of the Jura mountains is, for the most part, 
like that of the Oregon ridges in following the slopes of 
the deformed surface. Short streams run down the sides 
of the arches, cutting ravines on the slopes, as shown in 




Fig. 87. Diagram of the Jura, a Folded Mountain Range 

the unshaded foreground of Figure 87. Larger streams 
gather on the trough floors and escape at one end or the 
other as opportunity offers. Here and there a stream cuts 
across an arch, wearing a deep gorge from one trough 
valley to the next, and exhibiting the arched structure, as 
in the middle ridge of Figure 87. 

Where are the Jura mountains? How many arches are shown in 
Figure 87 ? How many troughs ? What is their trend ? How manv 
cross valleys ? If you were traveling there, where would you go to 



IVIOUNTAINS 185 

see the arched rock layers ? Where does the topmost layer lap over 
an arch ? What forms result where the topmost layer has been 
partly worn away ? Describe the course of some of the small streams 
that rise on the top of an arch. 

As in all mountains of diKstinct relief, the form of this 
range exercises a strong control over the distribution, 
occupation, and movement of the population. The valley 
floors are well settled ; villages often lie near the mouths 
of transverse gorges. Roads are generally limited to the 
lengthwise and crosswise valleys. Byways and footpaths 
lead to the upland fields and pastures. Little villages are 
sometimes found on the tops of the broader arches. The 
steeper slopes are generally forested. 

112. Lofty Mountains. — Lofty mountain ranges, like cer- 
tain parts of the Rocky mountains, but better represented by 
the Alps, the Caucasus, and the Himalayas, exhibit a remark- 
able variety of peaks, ridges, ravines, and valleys. Their 
higher central peaks usually consist of the most resistant 
rocks, surrounded by slanting layers that rise in great ridges. 

These majestic forms' usually depend as much on the 
deep erosion of great valleys by streams as on their lofty 
uplift. Unlike the simple tilted blocks of Oregon, or the 
orderly folds of the Jura, the greater ranges show little or 
nothing of their original form. 

The discovery of marine fossils in the bedded rocks of 
high Alpine ridges toward the close of the eighteenth cen- 
tury was received with great astonishment by the scien- 
tific men of the time. The occurrence of fossils in so 
elevated a position was one of the first generally accepted 
proofs of the changes that have gone on in the past, by 



186 



ELEMENTARY PHYSICAL GEOGRAPHY 



which the present form of the earth's surface has been 
fashioned. But not until the nineteenth century had well 
advanced was it generally understood how much more the 
form of lofty mountains depends on processes of land 
sculpture than on forces of uplift. 

113. Peaks and Ridges. — The height of lofty mountain 
summits is due in great part to the uplift that the whole 




Fig. 88. Peaks of the Central Alps 

range has suffered, but in part also to the success of the 
stronger rocks in resisting the attack of the weather, under 
which the weaker rocks have greatly wasted away. The 
waste that is shed from the peaks and ridges creeps and 
washes down into the valleys, usually leaving the loftiest 
summits bare and sharp. Deep valleys are eroded by the 
streams between the ridges, and steep ravines are worn in 
the slopes and spurs. Thus mountain forms are chiefly 
due to weathering and stream carving. 



MOUNTAINS 



187 



The bare rocky peaks and ridges, rising into the cold 
upper atmosphere, far above the limits of vegetation, are 
silent deserts. The stillness is broken only by the rush 
of storm winds and the roar of rock falls and snowslides. 
Not less barren are the snow fields and the talus slopes 
on the higher mountain flanks, and the slanting reservoirs 
of ice and snow in the upper valley heads, from which 




Fig. 89. An Alpine Peak of Slanting Layers 

slow-moving ice streams, or glaciers, creep down to the 
lower valleys. The lower slopes are generally forested. 

Many summits in the Alps are so sharp that they are 
called needles or horns. They rise as almost inaccessible 
peaks between the growing valley heads. Mt. Blanc, the 
highest mountain of the range (nearly 16,000 feet), is of 
domelike form with a heavy snowcap ; it is not yet suf- 
ficiently dissected by valleys to take the form of sharp 
ridges and peaks. 



188 ELEMENTARY PHYSICAL GEOGRAPHY 

The Selkirk range of the Rocky mountains in Canada 
has steep and bare summits surmounting the long lower 
slopes. The slopes are covered with waste that is slowl}^ 
creeping and washing into the valleys, to be borne awa}'^ 
by the streams. Having an abundant snowfall, the range 
bears extensive snow fields and glaciers. In the Rocky 
mountains of Colorado snow is less plentiful, snow fields 
are small, and glaciers are wanting. Long slopes of creep- 
ing waste cover the mountain flanks far up toward the 
summits, as in Plate I ; craggy peaks of sharp form are 
less common than in the Selkirks or the Alps. 

114. Climate of Mountains. — On extensive plains the 
climate — especially the temperature and rainfall — shows 
little variation from place to place, being nearly uniform 
for hundreds of miles together. On the average, one must 
travel from thirty to sixty miles poleward to find a differ- 
ence of 1° in mean annual temperature. The same differ- 
ence is found on mountains by an ascent of only 300 feet. 
Many mountains rise so high that they receive snow 
while rain falls on the surrounding lower lands. Lofty 
mountains are therefore usually clothed with snow on their 
higher slopes. 

Broad plains may have only a scanty rainfall over hun- 
dreds of miles together. On mountains the rainfall rapidly 
increases wdth elevation, although less may fall on very 
lofty summits than at heights of from 5000 to 10,000 feet. 
Not only because they are high, but also because they 
receive much rain and snow, high mountains are usually 
the sources of large rivers. 



I 



MOUNTAINS 189 

The small changes of form and climate over broad plains 
make the conditions of life nearly the same over great 
areas. A great diversity of form and climate is found in 
mountains within small distances, and strong contrasts are 
crowded close together. 

115. Mountains as Barriers. — High mountains serve as 
barriers separating the climates and the populations of their 
opposite sides. The windward (eastern) slope of the equa- 
torial Andes has a moist climate because the damp winds 
from the Atlantic, ascending and cooling, give forth a heavy 
rainfall there ; the western slope has a dry climate because 
the same winds, descending and warming by compression, 
not only give forth no more rain, but eagerly take up what- 
ever moisture they find on the way. The eastern slope is 
densely forested; the western slope is for the greater part 
a desert, except in valley floors watered by streams. 

Moist winds from the Pacific give a plentiful rainfall 
on the windward (westward) slopes of the Sierra Nevada 
and the Rocky mountains of the United States. The same 
winds, descending on the eastern or leeward slopes, become 
in winter unseasonably warm and dry, evaporating the light 
snow of the plains and laying bare the dry tufts of grass, 
greatly to the advantage of the cattle feeding there. The 
dry wind is called the chino ok. A similar wind occurs 
in the northern valleys of Switzerland, where it is called 
the foehn. 

The great popalations of India and China, representing 
different races, are separated by the Himalayas and other 
ranges in southern Asia. The two peoples are thus so 



190 ELEMENTARY PHYSICAL GEOGRAPHY 

well held apart that neither of them has had any important 
influence on the other. Lofty mountain ranges thus rank 
with the oceans in separating the inhabitants of the lands. 

When low countries on opposite sides of a high range 
are occupied by different peoples the mountains commonly 
serve as a natural boundary between them. The moun- 
tain range as a whole may serve as a rough boundary 
between uncivilized nations ; but between civilized nations 
the crest line dividing the rivers of the opposite slopes is 
often accepted as a more precise boundary, as in the 
Pyrenees between France and Spain, where the river 
divide is generally adopted as the national divide. 

When the river divide departs from the main range 
that it was supposed to follow before the mountains were 
explored, the boundary question may give rise to dispute, 
as recently between Argentina and Chile, where a number 
of Pacific rivers rise on the pampas of Patagonia and cut 
through the Andes in deep gorges. 

The difficulty of crossing lofty ranges gives great impor- 
tance to the notches, or passes, in their central ridges, 
through which travel and traffic may go with less effort 
than over their peaks. The heavy snows of the winter 
may close the passes for -several months. In earlier cen- 
turies, when the passes were traversed only by paths, 
houses of refuge were often maintained on the summit by 
monks, as on the famous pass of St. Bei"nard in the Alps. 

It is mostly within the last hundred years that well- 
planned roads have been constructed over the chief passes 
of various mountain ranges. The roads enter the moun- 
tains along the larger valleys and then zigzag up the 




Plate VII. A Railroad rounding a Spur of Mt. Ouray, Colorado 



MOUNTAINS 191 

steeper slopes. They are carefully laid out so as not to 
exceed a certain moderate grade, — about five feet in a hun- 
dred. Certain passes are now crossed even by railroads, 
the ascent from the valleys being most ingeniously made 
by curves and " loops." Sometimes the last part of the 
ascent is avoided by tunneling the ridge under the pass, 
it being cheaper in the long run for a railroad to bore 
through than to climb higher. 

When gold had been discovered in California and a new 
population was making its way there in 1849 and 1850, 
the mountain ranges in the western United States were so 
formidable a barrier to travel that many of the emigrants 
preferred the long voyage by sailing vessel around Cape 
Horn. Those who went overland suffered great hardships 
in crossing the mountains by rough trails, and many died 
on the way. Since then the mountains have been care- 
fully explored, the lowest passes have been found, and sev- 
eral railroad lines now connect the Central States with 
the Pacific coast. 

Mountains are often climbed for the exhilaration that 
comes from ascending them, and for the glorious view over 
the peaks and valleys that is gained from the summits. 
Clubs of mountain climbers have been formed in many 
countries. They publish narratives of excursions in 
mountainous regions. The ascent of very lofty moun- 
tains, above 16,000 feet in height, is made difficult by the 
thinness of the air so far above sea level. Fatal acci- 
dents sometimes occur, especially when inexperienced 
climbers try to make ascents of difficult peaks without 
well-trained guides. 



192 



ELEMENTARY PHYSICAL GEOGRAPHY 



116. Avalanches. — The heavy snowfall of winter often 
overloads the snow banks on the higher slopes, and great 
masses of snow slide down to lower levels. Summer melt- 
ing and rainfall also cause slides, or avalanches (a-val, to the 
valley). Sometimes the snow mass glides along the sloping 
surface at a moderate speed. Sometimes it leaps from cliffs 




Fig. 90. Path of an Ice Fall in the Alps 



and falls with a terrible velocity to the valleys below; a 
violent blast of air bursts outward from beneath, overturn- 
ing trees hundreds of feet beyond the reach of the snow. 

Certain villages in Alpine valleys carefully preserve a 
patch of forest on the slope above them as a protection 
from avalanches. Roads and railways on steep mountain 
slopes must here and there be covered in by long snow- 
sheds, over which the snow may slide without blocking or 
injuring the road. 

Heavy masses of ice are occasionally detached from 
glaciers that end on steep slopes, forming " ice falls." 



MOUNTAINS 193 

These are even more destructive than avalanches of snow. 
An ice fall over 5,000,000 cubic yards in volume broke 
from a glacier on the slope of a peak in the Alps in Sep- 
tember, 1895 (Figure 90 ; see Figure 89, from a photo- 
graph taken before the fall). It slid down a steep slope 
two and a half miles long, gathered about 1,300,000 
cubic yards of rock waste on the way, and then rushed 
across the valley floor, dashing far up the opposite slope 
and falling back again, like a wave from a cliff. A bench 
on the path of the sliding mass caused it to leap forward, 
clear of the ground; then, as it fell, the air beneath was 
violently driven away, blowing out fragments of ice and 
rock and breaking down trees hundreds of yards distant 
(shown by arrows turned to the right. Figure 90). 

117. Landslides on Mountainsides. — In deep and nar- 
row valleys among mountains the side slopes are sometimes 
cut so steep that great rock masses may be loosened from 
the walls and slip to the bottom, forming landslides. 

A landslide in the Alps in 1898 destroyed a few of 
the houses on the edge of the village of Airolo, near the 
southern entrance to the great St. Gotthard tunnel. The 
scar left by the falling mass is still distinctly visible high 
up on the mountain side ; the fallen rock, greatly shattered, 
spreads forward toward the stream in the valley floor. 
Had the slide taken a course a quarter of a mile farther 
south, it would have destroyed much of the village. 

In September, 1893, a great landslide occurred in the 
deep valley of one of the upper branches of the Ganges in 
the Himalayas. In three days 800,000,000 tons of rock 



194 



ELEMENTARY PHYSICAL GEOGRAPHY 



fell with deafening noise, darkening the air with dust, leav- 
ing a great bare cavity with steep walls several thousand 
feet high to mark its source, and building a dam nearly 1000 
feet deep across the narrow valley floor. A lake gradu- 
ally formed on the 
upstream side of 
the dam and grew 
to be four milies 
long before it over- 
flowed, about a year 
after the slide. 

In the meantime 
the danger that the 
lake might burst 
out in a great flood 
being perceived by 
the British engi- 
neers in charge of 
the public works of 
India, the bridges 
in the lower valley 
were removed; 
safety marks were 
set uj) on the valley 
sides, 100 or 200 feet above the ordinary river level, indi- 
cating the height above which the flood would probably not 
rise ; and a telegraph line was constructed down the valley 
from the dam, to give prompt warning of the outburst. 

The flood occurred at midnight, August 26-27, 1894. 
In four hours about 400,000,000 cubic yards of water 




Fig. 91. The Landslide of Airolo, Switzerland 



MOUNTAINS 



195 



were discharged, cutting down the dam nearly 400 feet, 
flooding the valley to a depth of from 100 to 170 feet, 
and rushing forward with a velocity of 20 miles an hour. 
Many miles of valley road were washed away. Every 




Fig. 92. A Laudslide ia the Himalayas 



vestige of habitation was destroyed in villages along the 
upper Ganges ; but so well was the notice of danger given 
that only one man lost his life, and that because he 
would not heed the warning. Under a less intelligent 
control, thousands of people must have perished in such a 
catastrophe. The remains of many other landslides are 
found in the valleys of the Himalaj^as. 



196 



ELEMENTARY PHYSICAL GEOGRAPHY 



118. Valleys among Mountains. — One of the strongest 
characteristics of thoroughly dissected, lofty mountains is 
the activity with which the rock waste is weathered from 
the peaks and cliffs, moved down the precipitous slopes, 




Fig. 93. The Himalaya Mountains 



swept by flooded torrents down steep ravines, and washed 
by streams along the larger valleys and out upon the 
adjoining lowlands. The waste seems everywhere to be 
streaming (as the long-lived mountains might say) down 



MOUNTAINS 197 

from the peaks and ridges. The carving of valleys in the 
mountains has been accomplished by the long duration of 
these active processes for ages jjast. 

The rock waste consists of angular fragments as it falls 
from the cliffs and creeps down the slopes. The angles are 
worn off as the waste is rolled along in rapid torrents, 
and after traveling thus for a few miles the fragments are 
well rounded, becoming smaller and smaller the farther 
they are swept along the stream bed. The fine grains 
that are worn off from the angles of the larger fragments 
are borne along more quickly than the larger pebbles and 
cobbles. 

A torrent that receives much coarse waste from a steep- 
sided ravine frequently sweeps so much of it into the main 
valley that it cannot all be carried away by the master 
river. The coarser part of the waste then accumulates in 
a conelike form, known as an alluvial fan^ spreading with 
even slope from the ravine mouth into the main valley. 

Alluvial fans have a steep slope when formed by small 
torrents bearing a coarse and plentiful load. They have 
a fiat slope when formed by large streams with a fine- 
textured load. They may grow to great size, with a 
radius of five or ten miles, in large valleys. 

Large fans drive the master river against the farther 
side of its valley, where it undercuts the valley wall. The 
fan still growing, the river may be obstructed and thus 
required to spread over the valley floor upstream from 
-the fan, forming a shallow lake, while on the downstream 
side the river descends in rapids over the coarsest bowlders 
brought down by the torrent. 



198 



ELEMENTARY PHYSICAL GEOGRAPHY 



How many fans are shown in Figure 94? Where has their 
material come from? How has it been brought? What effect 
have they on the course of the main i-iver? 

A torrent frequently changes its course on a fan and 

enters the main river 
at a new point. Two- 
Ocean creek, a small 
stream in the Yellow- 
stone Park, has built 
a fan that forms a 
part of the conti- 
nental divide. Some- 
times the stream flows 
on an eastern radius 
of the fan to Atlan- 
tic creek (Missouri- 
Mississippi system), 
sometimes on a west- 
ern radius, to Pacific 
creek (Columbia sys- 
tem). 

Villages are often 
built and fields are 
cultivated on fans of 
large size. When the torrent of such a fan is turned on 
a new course it may flood fields and villages, causing much 
damage. A valley road crossing the fan is swept away 
where the torrent then comes upon it, while the bridge 
over the former channel is useless, now that the torrent 
has abandoned it. 




Fig. 94. Alluvial Fans 



MOUj^TAINS 



199 



Accidents of this sort are common in mountain regions. 
In 1896 a stream entering a lake in Switzerland overflowed 
its fan with a stony flood fed by a landslip in the head 
ravine. It laid waste a strip two miles long and over 300 
feet wide at the forward end, covering it with a layer of 
stony mud ten or twelve feet thick. Houses were pushed 
out of place; a road and a railroad were buried. The 
advance of this curi- 
ous flood was some- 
times so slow that the 
grass on the fields in 
front of it was saved 
by hasty mowing. For 
a time all travel had 
to go by boat on the 
lake. The people who 
lived on the fan had 
some compensation 
for their losses in car- 
rying the thousands of visitors to and from the scene of 
the disaster. 

Sometimes the steep torrential headwaters wash so much 
waste from their ravines into the lower valley that the 
river is unable to carry along all that it receives. Some 
of the waste then gathers on the valley floor, gradually 
filling it higher and higher, as in Figure 95. Valley floors 
of this form are much more easily traveled upon than 
when the side slopes descend directly to the river bank. 

After mountain waste has in this way gathered in a val- 
ley to a considerable depth, sometimes measuring several 




Fig. 95. A Filled Valley with a Flat Floor 



200 



ELEMENTARY PHYSICAL GEOGRAPHY 



hundred feet, there may be a decrease in the amount of 
waste supplied by the headwater streams. This change 
will permit the river to turn part of its strength to sweep- 
ing away some of the waste in its bed, and thus to deepen 
its channel. As more and more waste is thus removed, 
a new valley comes to be opened in the flat valley floor, 
remnants of which then stand in benches or terraces above 

the new level of. the 
river, as in Figure 96. 
Terraced valleys of 
this kind are not un- 
common in the Rocky 
mountain region. 
Some of the inner 
valleys of the Hima- 
laya mountains have 
gravel terraces over 

Fig. t)G. A Terraced Valley 1^00 feet high. 




119. Lengthwise and Crosswise Valleys. — When a river 
has cut down its valley floor to as moderate a slope as the 
load of waste that it has to carry along will allow, it may 
still wear away its banks, first on one side, then on the 
other. Thus in the course of time the river broadens the 
valley floor. This is especially true in a valley that is 
worn down along a belt of weak rocks parallel to the gen- 
eral trend of a mountain range, for these rocks weather 
and wash away at a comparatively rapid rate. 

The crosswise valleys, by which the rivers of the long 
inner valleys find outlets through inclosing ridges, are 



MOUNTAINS 201 

often narrow and steep-walled gorges, for the ridge- 
making rocks are resistant and weather slowly. The 
floor of a crosswise or transverse valley may be hardly 
wider than its stream ; the walls rise steep from the 
water's edge, leaving little or no room for a road or path 
on either side. 

It is chiefly in the broader lengthwise valleys that 
mountain peoples dwell. When the outlet valleys are 
narrow gorges the outer world has for centuries been 
reached only by passes over the inclosing ridges ; but 
modern engineering skill has sufficed to build and cut 
roads and railroads through many gorges that were 
impassable a century ago. 

120. Earthquakes of Growing Mountain Ranges. — The 

process of bending and breaking the rock structures 
within a mountain mass is certainly very slow, but it 
sometimes causes sudden snaps and slips of a few inches 
or a few feet. Tremors then spread in all directions 
from the seat of disturbance, diminishing in force as they 
advance. On reaching the earth's surface they are felt as 
earthquakes, producing more or less destruction. Shocks 
of this kind are comparatively common in and near most 
of the lofty mountains of the world. 

Earthquake tremors travel through the earth's crust with 
great velocit}^, — from ten to forty miles a minute ; but, as 
in the case of water waves, the actual movement of the 
quaking earth at any point may be only a few inches or a 
few feet a second, backward and forward. The shocks 
produced by earthquake waves are most violent at places 



202 



ELEMENTARY PHYSICAL GEOGRAPHY 



directly over the seat of chief disturbance. They may be 
very faint, causing no damage. They may be strong 
enough to be felt violently over hundreds of square 
miles, less distinctly over many thousands, and very faintly 
(by the aid of delicate instruments) all over the earth; 




Fig. 97. Railroad shaken by an Earthquake, Northeastern India 



One of the greatest modern earthquakes occurred at 
the base of the Himalaya mountains in northeastern 
India in 1897. It was probably caused by some under- 
ground movement of mountain growth. It formed sev- 
eral fissures, displacing the land on one side with respect 
to that on the other, forming a step several feet high.. 
The vibrations of the shock loosened rock masses and 
soil on steep slopes, causing many landslides, which left 



MOUNTAIXS 



203 



the hillsides bare and clogged the valleys. Thousands of 
forest trees and a great number of buildings in the central 
area were broken down by being swayed violently back 
and forth, although the movement was only a few inches. 
Streams were obstructed and turned from their courses. 




Fig. 98. Land Surface displaced by an Earthquake, Japan 

Railroad tracks on the neighboring plains were thrown 
out of line. 

A violent earthquake occurred in Japan in 1891 by 
Avhich a deep fissure was formed in the earth's crust, 
and the land on one side of it was lowered with respect 
to that on the other, as shown in Figure 98. 

Earthquakes of moderate violence are still frequent in 
the Alps, occurring five or ten times a year. Five cen- 
turies ago (1348) a violent earthquake in the eastern 



204 ELEMENTARY PHYSICAL GEOGRAPHY 

Alps caused a great landslide by which a valley was 
barred across and a lake formed upstream from the slide. 
Countless thousands of shocks must have been produced 
during the long ages of mountain growth. The associa- 
tion of earthquakes with the young tilted-block ridges of 
Oregon, with the more mature mountains of Nevada, and 
with vigorous ranges like the Alps and the Himalayas, is 
a natural result of the continued disturbance or growth of 
the mountains. 

131. Human Life in Lofty Mountains. — The people 
who to-day dwell in the valleys of lofty mountains are 
in many cases the descendants of races who formerly 
occupied the adjacent lower lands, from which they 
Avere driven by conquering invaders. Inclosed valleys 
among mountains serve as refuges, where pursuit is too 
difficult to be profitable. There the weaker race long 
remains unmolested, holding little intercourse with the 
outer world and preserving old forms of speech and old- 
fashioned customs. The invaders occupy the neighboring 
open country ; they engage in traffic with other parts of 
the world and advance in new ways of living. 

122. Subdued Mountains. — There are certain mountain 
ranges of moderate height in which sharp peaks are absent 
and bold cliffs are rare. The slopes are of moderate steep- 
ness, and rock waste covers them almost from base to 
summit. Mountains of this kind do not reach upward 
into a climate very unlike that of their base ; and if 
not in a dry or a frigid region, they may be forest clad 
to the top. 



MOUNTAINS 205 

The earthquakes that are common in mountains of active 
growth and the landslides that happen frequently in moun- 
tains where the valley sides are still steep are rare or 
unknown in these mountains of gentler form. Unlike 
those vigorous and lofty younger forms in which uplift 
and erosion are still active, the rounded forms of these 
mountains express subdued strength, as if their high 
peaks and ridges had been greatly worn away by the long- 
continued attack of the weather. They may therefore be 
called subdued mountains. 

The Blue ridge and other mountains of North Carolina 
are good examples of subdued mountains. No sharp peaks 
tower into the sky. The summits generally rise dome- 
like in rounded outline. Heavy forests clothe their slopes. 

Subdued mountains may still have so strong a relief 
that the people living in their valleys preserve older 
fashions than those of the more open lower country. This 
is seen in the homespun clothing and in the primitive 
manner of living of the North Carolina mountaineers. 

The mountains of Wales make another group of sub- 
dued forms, but more rugged than the mountains of North 
Carolina. Here remain some of tlie descendants of the 
ancient Britons who were driven from the more open 
lowlands of eastern and central England by Saxon and 
Norman invaders, 1000 or 1500 years ago. The Welsh 
language, therefore, represents the original language of 
Britain, while the English language is a compound of the 
speech of the invading peoples from the continent. The 
Scotch highlanders are clannish because the clans have 
long lived in secluded glens among the Highlands. 



206 ELEMENTARY PHYSICAL GEOGRAPHY 

123. Worn-Down Mountains. — In certain parts of the 
world ancient mountain ranges have been almost com- 
pletely worn away. Their disordered rocks, once rising in 
lofty peaks and ridges, arid perhaps bearing snow fields and 
glaciers, have been reduced to an almost plain surface, little 
above baselevel and everywhere open to settlement. Low- 
lands of this kind are called peneplains (pene, almost). 



Fig. 99. The Piedmout Belt, Virginia 

The Piedmont belt of Virginia, between the Blue ridge 
and the coastal plain, is in many respects an excellent 
example of a worn-down mountain range. It is a pene- 
plain, not monotonously smooth, but undulating in graceful 
swells between gentle depressions. The soil is deep, fine, 
and fertile, and the district is very generally occupied by 
farms. The height to which the rock masses once rose 
above the present surface is reasonably estimated as at least 
one mile ; it may have been two or three. The wearing 
down of these ancient mountains to the rolling plain of 
to-day has required an enormously long period of time. 

It often happens that the plain surface of a worn-down 
mountain range is here and there surmounted bv rounded 



MOUNTAINS 



207 



hills or low mountains, 1000 or more feet bigh, composed 
of the most resistant rocks of the whole region. These 
hills are the last remnants of the mountains that once 
towered over. the surface of to-day. Several hills of this 
kind are scattered over the Piedmont plain of Virginia, 
one being shown in Figure 99. Such remnant hills and 




Fig. 100. Map of the Piedmont Belt, Virginia 

mountains are often called monadnocks, after an excellent 
example of their class in southwestern New Hampshire. 

It is generally the case that old-mountain lowlands are 
now uplifted above the position in which they stood when 
worn down, so that they form plateaulike uplands. Their 
streams are thus revived into a new period of activity and 
at once proceed to trench and dissect the upland. 

The Piedmont belt of Virginia now stands several hun- 
dred feet above baselevel. ^ It is cut across by a number 
of active streams that flow in rocky, steep-sided valleys 



208 ELEMENTARY PHYSICAL GEOGRAPHY 

from 100 to 300 feet below the upland plain. It must 
therefore be supposed that this region has been somewhat 
uplifted since its ancient mountains were worn down. It 
is in the valley sides that the tilted rock structures in the 
foundations of the ancient mountains are best seen. 

Southern New Hampshire and Vermont, central and west- 
ern Massachusetts, and aU of Connecticut include many 
uplands, above which occasional hills and low mountains 




Fig. 101. The Upland of New England, with Mt. Mouaduock in the 
Distance and a Valley in the Foreground 

rise, and below which numerous open valleys are worn. 
When an observer stands on the uplands the sky line is seen 
to be comparatively even. If the valleys were in imagina- 
tion filled up again to the level of the uplands, the worn- 
down peneplain of the ancient mountains of New England 
would be restored. 

The peneplain does not now stand so low as when it was 
worn down. It has been uplifted into a slanting position, 
so that it slowly rises from sea level at Long Island sound 
to a height of from 1400 to JLGOO feet on the northern 
boundary of central and western Massachusetts. The 



MOUNTAINS 



209 



valleys have been carved because the old lowland has been 
lifted up. They are shallow near the coast, but deep (800 
to 1000 feet) in the interior, where the upland is higher 
above baselevel. They are comparatively narrow where 
the rocks are so resistant that they weather slowly, but 
wide open where the rocks are weaker. The chief of 
the wider valleys is that of the Connecticut river, a 




Fig. 102. Valley of the Deerfield in the New England Upland 



broad lowland excavated along a belt of relatively weak 
-sandstones. 

The uplands have a scattered farming population, here 
and there gathered in small villages. The larger valleys 
contain many villages and cities, and guide the chief roads 
and railroads. Here is gathered the more active manu- 
facturing and commercial population of New England. 



210 



ELEMENTARY PHYSICAL GEOGRAPHY 



124. Old Mountain Ridges. — The Allegheny mountains I 
of Pennsylvania and Virginia consist of a number of nearly j 
parallel ridges with remarkably even crest lines, here and ^ 
there cut down by the notches or water gaps of streams I 
and rivers. The strata of these mountain belts are strongly \ 




Fig. 103. Diagram of the Allegheny Mountains, Pennsylvania 

folded, so that, if unworn, they would rise in great arches, ' 
as in the background of Figure 103. 

But it is now so long since the strata were pressed 
into folds that they have been worn down to a low 
peneplain at the level of the dotted line AB, in the fore- 
ground of Figure 103. The peneplain thus formed has 
been uplifted one or two thousand feet ; the weaker 
strata have been again worn down, forming open valleys 
and leaving the harder strata standing in relief, as 



MOUNTAIXS 211 

even-crested ridges. The waste from the open valleys 
has been washed out through the notches that have been 
slowly cut down where the streams flowed across the 
harder strata. 

Plate IX shows one of these ridges in Maryland, with 
a notch cut through it by a bianch of the- Potomac river- 
How many notches are shown in Figure 103? 

125. Embayed Mountains. — If a mountain range near a 
continental border is lowered, it will be partly covered by 



Fig. 104. Model of Embayed Mountains 
Compare Figures 60, 62, and 104. Compare Figures 71 and 104. 

the sea. The effect thus produced will be similar to that 
observed in the half -drowned coastal plain already described. 
The valley floors and mountain flanks will be submerged 
to a greater or less depth, and many long bays will enter 
between outstretching promontories and islands, as in 
Figure 104. Islands of this kind are called continental 
because of their close relation to the neighboring land. 



212 ELEMENTARY PHYSICAL GEOGRAPHY 

The coast of British Columbia and. southern Alaska is 
bordered by high mountains, into whose valleys the sea 
now enters in long and deep passages, called fiords. Lat- 
eral ridges, separated from the mainland by water chan- 
nels or sounds, stand forth as islands. A navigable "inner 
passage," well protected from the rough water of the open 
ocean, is thus provided for steam vessels. The steep moun- 
tain sides, descending rapidly beneath the sea, generally 
offer no flat ground for settlement ; but most of the fiords 
now contain delta plains where streams enter their heads ; 
here villages find convenient sites. 

The coast of Maine, part of the dissected upland in the 
old mountain region of New England, has been partly sub- 
merged, so that it is entered by many long arms of the 
sea and fringed by many islands. Exl3ellent harbors are 
thus provided, and many of the people living near the 
coast are sailors and fishermen. 

QUESTIONS 

Sec. 108. "What is a mountain range? a mountain system? 
How do mountains differ from plateaus? What is the action of 
mountain-making forces? State a theory of their origin. How do 
streams affect mountain form ? To what two processes is mountain 
form due ? 

109. Describe an example of block mountains. Where are good 
examples of this class found ? How has the form of these moun- 
tains been produced? How do the forms of several blocks vary? 
What can be said of the age of these mountains? Why may it be 
believed that these mountains are still growing? Describe the 
drainage of these mountains. Consider the climate of the region. 
Describe the places of settlement. 



MOUNTAIXS 213 

110. Describe the dissected ranges of Nevada. Compare thein 
with the block mountains of Oregon. Ai-e the Nevada ranges still 
growing? Compare the climate of the ranges of Nevada and of 
Oregon. Describe the streams of the Nevada ranges. Where are 
settlements found among these ranges? 

111. Where are the Jura mountains? AYhat is their structure? 
How have these mountains been produced ? How is their sti'ucture 
related to their form ? What changes have been produced by erosion? 
Describe the drainage of these mountains. Compare the side ravines 
and the crossing gorges. State the location of villages and roads. 

112. 113. Name some lofty mountain ranges. Upon what two pro- 
cesses does the form of these mountains depend ? Compare the import- 
ance of land sculpture in these ranges and in the block mountains of 
Oregon. Of what do the lofty peaks and ridges consist? What 
becomes of the waste from them? What is the origin of the deep 
valleys ? Compare the domes and the horns of the Alps. Compare 
the Selkirk range of Canada and the Rocky mountains of Colorado. 

114. Compare plains and mountains as to variation of tempera- 
ture ; of rainfall ; as to conditions of life. Why are the sources of 
large rivers often found in mountains ? 

115. How do mountains act as barriers ? Compare the two slopes 
of the equatorial Andes as to climate and vegetation. What 
influence is exerted on climate by the Sierra Nevada and the Rocky 
mountains ? What is the chinook wind ? the foehn ? How have 
the Himalayas acted as barriers between nations ? How do mountain 
ranges serve as national boundaries ? Give examples. Explain the 
importance of passes. How are roads and railroads built over moun- 
tains? Give an illustration of mountains as an obstacle to travel. 

116. 117. What are avalanches? How are they caused? How 
do they move ? How are villages and roads protected from them ? 
Describe an ice fall in the Alps. What is a landslide? Describe 
the landslide of Airolo in the Alps ; of the upper Ganges in the 
Himalayas. What disaster followed the latter landslide? How 
were its dangers lessened ? 



214 ELEMENTARY PHYSICAL GEOGRAPHY 

118. Describe the movement of rock waste in mountains. How 
is the form of the waste fragments changed ? What is an alluvial 
fan? How is it formed ? How does the form of alluvial fans vary ? 
How do fans affect the course of a river in front of them ? How 
does the course of a torrent vary on its fan ? Describe Two-Ocean 
creek. To what dangers are villages and roads on fans exposed ? 
Describe an example from Switzerland. Describe and explain a 
waste-filled valley. Describe and explain a terraced valley. 

119. How are valleys widened? What sort of valleys are wid- 
ened most easily ? Describe crosswise valleys. Compare lengthwise 
and crosswise valleys as to occupation. 

120. What is an earthquake ? How are earthquakes related to 
mountains? How fast do earthquake tremors travel? How much 
movement may they cause? Where are the shocks felt most vio- 
lently? How far may they be felt? How often do earthquakes 
occur in the Alps? Describe the great earthquake of India, 1897. 
What effect was produced by an earthquake in Japan in 1891 ? 

121. Compare the people of mountains with those of the neigh- 
boring lowlands. 

122. Describe subdued mountains as to height, form, rock 
waste, earthquakes, landslides. Describe an example of this class. 
What effects have these mountains on their inhabitants ? 

123. What is meant by worn-down mountains ? What is a pene- 
plain ? Describe an example in Virginia. What is a monadnock ? 
Describe and explain the valleys of the Virginia Piedmont belt. 
Describe and explain the uplands and valleys of southern New 
England. How do they influence the distribution of population? 

124. Describe the Allegheny ridges as to form ; as to origin ; as 
to drainage. What is a water ga^s ? 

125. Describe the appearance of embayed mountains. What is 
their origin? What is a continental island? Describe the coast of 
southern Alaska ; the coast of Maine. 



CHAPTER VII 
VOLCANOES 

126. Volcanic Eruptions. — Most of the processes of 
nature go on without violence. The usual movements 
of the winds and currents, the flow and ebb of the tides, 
the rise and fall of the lands, the weathering and wash- 
ing of rock waste are so placid that we gain confidence 
in the earth as a safe home to live in. But sometimes 
natural processes of a more violent behavior are witnessed. 
Hurricanes and tornadoes bring destructive winds and tor- 
rential rains, flashes of lightning and peals of thunder. 
Landslides rush down mountain sides, overwhelming the 
valleys below. Now and then the rocky crust beneath 
us quivers and trembles in earthquakes. Great waves 
occasionally roll in from the sea and sweep over low 
coastal lands. Here and there volcanoes burst forth 
with terrible commotion. Nature then seems frightful 
and destructive. Those who are overtaken by such dis- 
asters struggle against them, hopefully awaiting the return 
of the more peaceful conditions under which their habits 
of life have been formed, for man could not survive if 
he were always battling against the wilder forces of 
nature. 

Of all natural catastrophes, the explosive eruption of 
a great volcano is the most terrible. The air resounds 

215 



216 ELEMENTARY PHYSICAL GEOGRAPHY 

with its roaring. The sky is darkened and the sun is 
hidden by clouds of dust blown from the crater. The 
sea is burdened with floating ashes. Glowing streams of 
molten rock, or lava, flow down the flanks of the volcano, 
driving away everything that can take flight before them. 
Even the earth around trembles as the gases and lavas 
burst out from their deep sources. No wonder that igno- 
rant races of men have imagined struggling giants to be 
imprisoned under active volcanoes, nor that even the most 
learned are baffled when trying to account for these ter- 
rific displays of natural forces. 

But violent as a volcanic eruption may be, it weakens 
and in time ceases. The sky clears, the sun shines again, 
and nature once more goes on with her more quiet tasks. 
As the years pass by and a soil is formed on the weath- 
ered lavas, plants clothe their surface and man comes to 
dwell on the flanks of the volcanic mountain. The erup- 
tion is forgotten ; fields and villages occupy the volcanic 
slopes ; little remains to tell of the commotion of former 
times. 

127. Young Volcanoes. — Volcanoes are formed by the 
ascent of molten lava through fractures or passages lead- 
ing from unknown depths beneath the earth's crust to its 
surface, on the land or on the sea floor. Although the 
lava is very hot, it is not burning or flaming. A volcano 
should never be described as a burning mountain. 

It is believed by many that the ascent of molten lava 
from its deep source is chiefly caused by pressures similar 
to those which cause movements in the earth's crust in 



VOLCANOES 



217 



mountain building, 



As the lava nears the surface and meets 
water in greater or less quantities, explosions of steam and 
other heated gases take a violent part in the eruptions. 




Fig. 105. Vesuvius iu Eruption 



The early growth of a volcano has occasionally been 
observed. The outburst is preceded and accompanied by 
earthquakes, which indicate the breaking of an upward pas- 
sage through the underground rocks, before hot lavas make 
their appearance at the surface. When the eruption is 



218 



ELEMENTARY PHYSICAL GEOGRAPHY 




Fig. 106. Monte Nuovo 



accompanied by gaseous explosions much of the lava is 
blown into fragments, of which the smaller are called 
ashes or cinders. The larger blocks and the coarser 
ashes accumulate in a conical heap, or volcano, frequently 
having remarkable regularity of form, a cup-shaped hollow 
or crater being kept open at the top over the vent by 
the outbursting gases. The finer ashes or dust may fall 

far away. When the 
eruption is less vio- 



lent the lava runs 
^^M forth more quietly in 
a stream or flow, fol- 
lowing the slopes of 
the ground. Explo- 
sive and quiet erup- 
tions may alternate in irregular succession, and after many 
eruptions the volcano may become a lofty mountain, one 
or two miles high^ 

Monte Nuovo (new mountain) is a small volcano that 
was formed on the north side of the Gulf of Naples 
in Italy in 1538. Earthquakes occurred thereabouts 
for two years before the eruption, when in a week's 
time a cone was built up 440 feet high, half a mile in 
diameter at the base, and with a crater over 400 feet 
deep. Masses of lava " as large as an ox " were shot 
into the air by the bursting of great bubbles of gas or 
steam that ascended through the lava in the vent. Finer 
ashes fell over the country for several miles around. 
The people of the neighboring villages fled in terror 
from their homes. 



VOLCANOf:S 219 

A greater eruption took place in Mexico in 1759, when 
the volcano JoruUo (pron. Ho-rul-yo) was built on the 
central plateau, burying fertile fields of sugar cane and 
indigo. The outburst was preceded by earthquakes; the 
eruption continued half a year, building six cones and 
pouring out extensive lava flows. The highest cone, 
Jorullo, rose 700 feet above the plateau. The flows 
retained a perceptible heat for over twenty years. 

Many examples might be given of marine eruptions. 
In 1867 a shoal was discovered among the Tonga islands 
of the Pacific (lat. 20° 20' S., long. 176° 20' W.), the 
surrounding sea floor being about 1000 fathoms deep. In 
1877 smoke was seen ascending from the sea surface over 
the shoal. In 1885 an island had been formed two miles 
long and 200 feet high. At this time a terrific eruption 
was in progress, and the shocks of the explosions were felt 
on neighboring islands. As the island consisted chiefly 
of ashes, it has since been rapidly eroded by the waves 
and will soon disappear, unless new eruptions occur. 

Most volcanoes have not been observed in their early 
growth, yet, even if not now in eruption, so perfectly do 
they correspond in form and structure with such examples 
as Monte Nuovo and Jorullo that no doubt can remain as 
to their origin. 

In northern California there is a cinder cone of remark- 
ably perfect form. Its barren slopes of loose ashes rise 
640 feet to the rim that incloses a crater 240 feet deep. 
A stream of lava has issued from near the base of the cone, 
flooding a neighboring valley with a lava field a mile wide 
and nearly three miles long. The surface of the field is 



220 



ELEMENTARY PHYSICAL GEOGRAPHY 



so covered with unweathered angular blocks of lava as to 
be almost impassable. The edge of the field is a steep 
and ragged slope 100 feet high. It obstructs a stream from 
the south, which forms Snag lake, so called from the dead 
trees still standing in it. On all sides the surface of the 
country is covered with a layer of volcanic ashes and dust, 
six or more feet deep near the cone, thinner and finer 
farther away, yet recognizable at a distance of eight miles. 




Fig. 107. Cinder Cone and Lava Flow, California 

From the size of trees growing on the ashes it is estimated 
that the cinder cone was built about 200 years ago. The 
lava flow is younger, but none of the Indians or early 
settlers thereabouts (1845) observed its eruption. 

128. Great Volcanoes. — Many large volcanoes, whose 
first eruption must have occurred many thousands of years 
ago, are still active. After long periods of more or less 
complete rest they burst forth again for a short time, 
blowing out showers of ashes, building their cones to a 
height of 10,000 feet or more, and adding new lava streams 
to their flanks, so as to gain a diameter of ten or twenty 
miles or more at the base. The melted lava often breaks 



VOLCANOES 



221 




forth from the mountain side and flows down to gentler 

slopes on the flanks and out upon the surrounding country ; 

thus the cone as a whole comes .-•-—. 

to have a rudely bedded struc- 
ture of ashy and dense lavas. 
It sometimes happens that 

the upper part of a volcano is 

destro3'ed by a violent eruption 

or broken in by underground 

disturbance, forming a greatly 

enlarged crater, or caldera. 

Volcanoes of this form are some- 
times called ring mountains. 
Deception island, in the 

South Shetland group, beyond 

Cape Horn, is the high rim of 

a caldera, breached on one side 

by a narrow gap, which gives entrance to a quiet circular 

bay. Layers of ice 
are to be seen between 
beds of ashes and lava 
on the caldera walls. 
The cone of Vesu- 
vius has been built in 
TT -.nn r^x r. f^T ■ ■ ^1 n ^^ alargc caldcraof morc 

Fig. 109. The Cone of Vesuvius m the Caldera » 

of Monte Somma (looking uorth) ancient Origin. The 

cone buries one side of 
the caldera lim, the other side being known as Monte Somma. 

Draw a map of A'esuvms and Monte Somma, like the map of 
Deception island in Figure 108. 



Fig. 108. Deception Island, a Vol- 
canic Caldera (plan and section) 




222 



ELEMENTARY PHYSICAL GEOGRAPHY 



Mt. Mazama, a superb ring mountain in Oregon, eon- 
tains a beautiful lake in its huge caldera. This volcano 
must have been once several thousand feet higher than it 
is now, before its upper part was engulfed in the formation 
of the caldera. 

Figures 110 and 115 are maps of Mts. Mazama and Shasta, in which 
the mountain form is indicated by lines that cui've around the slopes 
at definite heights, every line following a level course, and every pair 




Fig. 110. Contour Map of Crater Lake iu Mt. Mazama, Oregon 

of lines differing in height by a fixed amount. Lines of this kind 
are called contour lines, and the maps are contour maps. Where the 
lines are open spaced, the slopes are relatively gentle ; where the lines 
are close together, the slopes are steep. Compare the inward and out- 
ward slopes of the ring of Mt. Mazama; compare the upper and lower 
slopes of Mt. Shasta. Determine from Figure 110 the diameter of the 
caldera, and the average height of its rim above sea level and above the 
lake surface. 



VOLCAXOES 223 

A rough classification of volcanoes groups them as 
active, when they are frequently in eruption ; dormant 
(sleeping), when now at rest, though giving signs in hot 
springs and sulphurous vapors that activity may be begun 
again; and extinct, when they give no sign of activity. 
It is not possible to make certain distinction between the 
last two classes ; great eruptions have taken place in vol- 
canoes after all signs of activity had ceased. 

Showers of ashes as they chance to fall may bury villages, 
fields, and forests. The <listurbance in the atmosphere dur- 
ing a violent eruption often causes rainfall. The floods 
thus caused may be increased by the water from melted 
snow on the upper slopes of a lofty cone, and occasionally 
by hot water thrown out from the crater itself. The floods 
gather the fresli-fallen dust and ashes, producing muddy 
torrents that ovenvhelm the lower lands. 

At the eruption of Conseguina, Central America, in 
1835, ashes destroyed trees and dwellings twenty-five miles 
south of the volcano ; thousands of cattle and innumerable 
wild animals and birds were killed. Lava blocks ui frag- 
ments five or more feet in diameter are strewn for ten or 
fifteen miles around the great cone of Cotopaxi, Ecuador. 

A tremendous eruption of Galung-gung, a forested vol- 
cano in a populous part of Java, took place in 1822 ; 
torrents of hot water, mud, and ashes rushed down the 
valleys, flooding the rivers and drowning a great number 
of men and animals ; for twenty-four miles not a trace of 
numerous villages and plantations was left. 

The first recorded eruption of Vesuvius, A.D. 79, dark- 
ened the sky with its clouds. The ancient city of Pompeii 



224 



ELEMENTARY PHYSICAL GEOGRAPHY 



was buried in ashes and about 2000 persons (estimated at 
one fifteenth of the population) were killed. Herculaneum, 
near by, was overwhelmed with torrents of ashy mud. 
After being loug forgotten and overgrown by modern 




Fig. 111. Excavations in Herculaneum 

villages, parts of these cities have been laid bare by recent 
excavations, affording many illustrations of ancient archi- 
tecture and of ancient modes of living. The walls in the 
foreground of Figure 111 are the ruins of houses in ancient 
Herculaneum. They were buried to the level LL. 

129. Earthquakes in Volcanic Districts. — The shocks of a 
violent eruption may shatter the volcano, breaking its sides. 



VOLCANOES 225 

The earthquakes thus caused are felt for many miles around 
the volcano. The exploding gases produce thundering 
sounds, sometimes audible for hundreds of miles. 

In the remarkable explosion of the volcanic island of 
Krakatoa, already referred to (page 27), half the island was 
destroyed, leaving water more than 1000 feet deep where 
high land had stood before. The air Avas shaken so vigor- 
ously by the explosion that windows were broken a hun- 
dred miles away. Huge sea waves rolled away from the 
exploded island, causing great destruction on neighboring 
coasts. Pumice, or light spongy lava, formed a floating 
layer on the sea surface, obstructing the course of vessels. 
The dust blown out of the volcano darkened the air for 
hundreds of miles around. As the dust was spread far 
and wide by the upper atmospheric currents, it increased 
the brilliancy of sunset and sunrise colors. The famous 
" red sunsets " thus produced were visible in all parts of 
the world before the end of 1883 ; then, as the dust settled, 
their brilliancy gradually decreased. 

Besides the earthquakes directly produced by the explo- 
sive eruptions of volcanoes, it is probable that many other 
earthquakes in volcanic districts are the result of disturb- 
ances within the crust of the earth not directly connected 
witli volcanic action. The numerous earthquakes of Japan 
and Italy sometimes accomjDany eruptions, but are more 
frequently independent of all visible eruptive action. 

Great destruction is caused by earthquakes in regions 
that are frequently shaken. In the thickly populated dis- 
tricts of southern Italy many thousands of lives have been 
lost in the violent earthquakes of the last three centuries. 



226 ELEMENTARY PHYSICAL GEOGRAPHY 

130. Distribution of Volcanoes. — Volcanoes generally 
occur near the seacoast or on the sea floor, but a considerable 
number of cones and flows are known far in continental 
interiors. Volcanoes are more numerous on tlie lands bor- 
dering the Pacific ocean and the mediterranean seas than 
on the coasts of the Atlantic, but many volcanic islands are 
known in the Atlantic, as well as in the Pacific and Indian 
oceans. It is estimated that over 300 volcanoes are now 
active, about 100 of these standing on the continents. All 
high islands of small area, far from the continents, and many 
such islands near the continents are of volcanic origin. 

Extinct volcanoes are sometimes found far inland. 
Cinder cones and barren lavas are known on the plateaus 
of Arizona, 300 miles from the ocean; in Colorado, 800 or 
more miles inland; in Tibet, 500 or more miles inland. 
Several active volcanoes in Mexico, Central America, and 
elsewhere are so far from the coast that direct connection 
with sea Avater should not be regarded (as it has been) 
necessary to eruptions. 

Active volcanoes in the interior of continents are rare, 
but a large one is known in central Africa, noi'th of Lake 
Tanganyika, 700 miles from the Indian ocean. 

Islands formed by the growth of volcanoes in mid ocean 
are often bordered by Avave-cut cliffs, so that it is almost 
impossible to find a landing place on their shores. Being 
of rugged form and nearly inaccessible, as well as distant 
from the continents, they are all the more lonesome. 

A remarkable instance of the effect of isolation on the 
occupants of a remote volcanic island is seen in the language 
of the people of Iceland. Icelandic, Norwegian, Swedish, 



VOLCANOES 



227 



and Danish were all one language a thousand years ago : 
but while the isolated Icelandic has preserved its ancient 
form with slight change, the languages of the continental 
countries have been much modified ; that of Denmark 
especially having been affected by the neighborhood of 
Germany. 

131. Lava Flows. — Great flows of lava sometimes 
run beyond the base of the volcano in which they break 
forth. Their surface is comparatively smooth if it remains 




Fig. 113. Lava Flows on the Plateaus of Arizoua 



unbroken after first cooling, but extremely ragged and 
angular if the first crust is repeatedly broken by con- 
tinued movement. The edge of a ragged flow may 
form a bluff 100 feet or more in height. On one of the 
plateaus of Arizona near the Colorado canyon stands a 
throng of volcanic cones, from which broad streams of 
lava descend the bordering cliffs in black cascades and 
form barren lava floods on a lower plateau near by. 



228 ELEMENTARY PHYSICAL GEOGRAPHY 

In 1783 a great flood of lava rose from a deep fissure 
in Iceland, the lava issuing tranquilly for the most part, 
flowing away in vast sheets on each side, and advancing 
in streams far along the lower valleys. Hundreds of 
small cones were built over the fissure, which was twenty 
miles long. In the course of ages successive lava floods 
of this kind have built up broad uplands in the plateau of 
Iceland, the loose slaggy cones of earlier eruptions being 
gradually buried under later sheets. 

Two lava streams of the eruption of 1783 in Iceland 
flowed down valleys forty-five and fifty miles from their 
source, gaining a depth of several hundred feet where the 
valleys were narrow, and spreading out in lakelike plains 
where the valleys were open. The water of side streams 
was dammed and rose in lakes. Twenty villages were 
destroyed by the floods of lava or water; 9000 persons 
(about one seventh of the island's population) and a great 
number of cattle perished, not only at the time of the 
eruption, but afterward during a famine caused by the 
burial of the pastures and by the desertion of the coast 
by fish. 

The form assumed by successive lava flows in building 
a plateau is sometimes imitated on a cold winter night 
when trickling streams of water, suj^plied by daj'time 
thawing, are frozen as they advance. If the water is arti- 
ficially colored, successive flows are made plainly visible. 

Lava floods thousands of square miles in area have 
been poured forth in Idaho, Oregon, and Washington, 
Avhere they form an extensive plateau in a broad depres- 
sion among the surrounding mountains. 



VOLCANOES 



229 



Between the Columbia and Snake rivers, in eastern 
Washington, the plain surface of the lava flood meets the 
inclosing mountains just as the sea meets a half-drowned 
mountain range. The lava forms level bays between the 
ridges ; the ridges stand forth like promontories ; outstand- 
ing peaks rise like islands over the plain. A rugged moun- 
tainous basin has thus been converted into a plateau. Pai't 
of the lava plain has been uplifted in domelike form to a 
greater height than the rest and is now deeply dissected 
by the canyons of Snake 
river and its branches. 
This part is called the 
Blue mountains, i>, Fig- 
ure 114. 




Fig. 114. The Lava Plateau of Idaho, 
Oregon, and Washington 



132. Dissected Volca- 
noes. — Torrential streams 
running down the slope 
of volcanic cones carve 
ravines on their flanks. 
Many ravines are formed 
during the periods of rest in the growth of great volcanoes, 
only to be filled again by later eruptions of lavas and 
ashes. After eruptions cease the ravines deepen more and 
more, leaving sharp ridges between them, and at last dis- 
secting the cone so deeply as to leave little appearance of 
its original shape. 

Mt. Shasta, in northern California, is furrowed on all 
sides by gigantic ravines, but its conical form is still well 
preserved, Figures 115, 116. Many meadows about its 



230 



ELEMENTARY PHYSICAL GEOGRAPHY 



base mark the sites of lakes formed by laya-flow barriers 
but now filled and drained. The best agricultural land 
in the region is of this origin. 




Fig. 115. Contour Map of Mount Shasta, California 

A number of extinct and more or less dilapidated vol- 
canic cones surmount the plateaus of Arizona and New- 
Mexico, Mts. San Francisco and Taylor being among the 
best examples. 

Before the summit of Mt. Mazama was destroyed by 
engulfment its height was probably about equal to that 



VOLCANOES 



231 



of Mt. Shasta to-day. Ravines like those of Shasta had 
been worn down the slopes of Mazama; their lower 
courses are still seen on the outer slopes of the ring 
mountain, but their upper courses are lost. 

Many great volcanoes in various stages of activity and 
dissection are found in the Andes along the western side 
of South America. 




Fig. 116. Mount Shasta 

133. Geographical Changes caused by Volcanoes. — The 

construction of large volcanoes by successive eruptions 
sometimes causes curious changes in the course of rivers, 
whose valleys are more or less blockaded by the new-built 
cones. 

A remarkable example of this kind is found in Central 
America, where the growth of a range of volcanoes has 
transformed a bay that once opened to the Pacific into a 
lake, known as Lake Nicaragua. The volcanoes formed so 



232 



ELEMENTARY PHYSICAL GEOGRAPHY 



effective a barrier that the lake surface is now 105 feet 
above sea level and its outlet flows across what used to 
be the continental divide and discharges into the Carib- 
bean sea. Since the outlet took this course it has eroded a 




Fig. 117. Map of the Lake Nicaragua District 

deep gorge across the divide, and the level of the lake is 
now lower than when the eastward overflow first took place. 
This lake would form part of the proposed interoceanic 
canal route across Nicaragfua. 



Draw a map, based oh Figure 117, to show the genera] outline of 
the land before the volcanic range was built. The original outline 
of the bay now closed by the volcanoes and their lava flows is shown 
by a dotted line. Describe the changes caused by the building of 
the volcanic range. 



VOLCAXOES 233 



QUESTIONS 

Sec. 126. Give examples of the quiet processes of nature; of the 
violent processes. Describe the explosive eruption of a volcano. 

127. How are volcanoes formed? What is the most probable 
cause of the ascent of lava in volcanoes ? What is the effect of 
steam? Describe the early growth of a volcano. Give an example 
from near Naples ; from Mexico ; in the Pacific. Describe the cin- 
der cone in California. How did its lava flow affect a neighboring 
stream ? Why is this volcano thought to be of recent origin ? 

128. How are great volcanoes formed? What size do they 
attain? What is a caldera? Describe Deception island ; Vesuvius 
and Monte Somma ; Mt. Mazama and its caldera. How may volcanoes 
be classified ? What effects may be produced by showers of ashes ? 
by floods? How may these floods be caused? Describe some inci- 
dents of the eruption of Conseguina, 183.5 ; of Cotopaxi; of Galung- 
gung. What can you tell of Pompeii and Herculaneum? 

129. Why are earthquakes often associated with volcanoes? 
Describe the explosion of Krakatoa. 

130. How are volcanoes distributed? Compare the Atlantic and 
Pacific in this respect. How many active volcanoes are known? 
How many of these are on the continents ? Where are volcanic 
islands found ? What forms have they ? Where are extinct vol- 
canoes often found? Where is an active volcano found far inland? 
Give an instance of the effects of living on a remote volcanic island. 

131. Describe the surface form of lava flows. Describe the lava 
cascades near the Colorado canyon ; the erujition and lava flood of 
1783 in Iceland; the lava floods of Idaho. 

132. Describe a dissected volcano. Name some examples of this 
class. Compare Mts. Shasta and Mazama. 

133. What geographical changes may be jiroduced by volcanoes ? 
Describe an example of such changes in Nicaragua. 



1 



CHAPTER VIII 
RIVERS AND VALLEYS 

134. Underground V/ater The water supplied by rain 

and snow is disposed of in part by evaporating from the 
surface, in part by running down the slopes of the land 
to the streams, and in part by sinking underground. The 
latter part is called underground water, or simply ground 
water. 

The proportions of these several parts vary under 
different conditions. The greater part of a light and 
long-continued rain may pass underground, especially if 
falling on a plain. A very heavy rain, or " cloud-burst," 
falling on strong slopes is largely disposed of by direct 
run-off, causing sudden floods. 

Rain, falling on a surface having a deep soil well cov- 
ered with vegetation (grass, bushes, or forest), will for the 
most part soak into the ground. On arid plains a great 
part of a light rain may dry off from the barren surface of 
the ground, but a heavy rain will run off in a flood. 

Loosely consolidated strata and deep rock waste take 
in much ground Avater. Firm rocks, such as granites, 
allow but little water to enter beneath the weathered 
waste on their surface. When the ground is frozen little 
water can enter it ; hence rivers rise in floods when deep 
snow is rapidly melted by a heavy rain. 

234 



RIVERS AND VALLEYS 



235 



Underground water is essential to the growth of plants, 
whose roots must reach moist earth. Where grass and 
trees cover the surface, much ground water taken in by 
their roots is discharged into the air by evaporation from 
their leaves. 




Fig. 118. Diagram of Cavern and Sink Hole 



135. Caverns. — Most rocks are not soluble in water. 
Limestone is exceptional in this respect ; it may be slowly 
dissolved, especially 
by ground water, 
which gathers cer- 
tain acids from 
decomposing vege- 
tation as it soaks 
down through the 
soil. Caverns in 
limestone districts 

are the result of this solvent action of underground waters. 
The Mammoth cave of Kentucky and the Luray cavern of 
Virginia are famous examples of their class. Streams 
gathering on the surface descend to underground pas- 
sages by hollows, known as sink holes or swallow holes. 
After flowing underground for some distance such streams 
may issue m enlarged and turbid currents from the mouths 
of caverns. 

Where sink holes and cavern drainage prevail so much 
water enters the ground that surface streams are compara- 
tively rare. When the sink holes or the underground pas- 
sages become obstructed ponds and lakes are formed in 
the surface basins. 



236 ELEMENTARY PHYSICAL GEOGRAPHY 

Several species of animals dwelling in the complete 
darkness of caverns are blind, but their senses of hearing 
and touch are highly developed. 

As the cavern enlarges, its roof may fall in more or less 
completely. The beautiful Natural bridge of Virginia is 
the remnant of a cavern roof. 

136. Springs. — Very little ground water remains per- 
manently beneath the land surface. Sooner or later, after 
descending to less or greater depths, it returns to the sur- 
face at a lower level than where it entered, coming out in 
the form of springs and joining the run-off of streams. 

The movement of ground water is comparatively slow 
while percolating among the particles of rock waste or 
through the pores and crevices of rocks. Where a large 
part of the rainfall enters the ground, the volume of the 
streams fed by springs is less variable than where the rain- 
fall is mostly discharged by direct run-off during and 
shortly after a storm. 

It is for this reason that the springs and streams of a 
forested region usually have a comparatively constant flow ; 
but this rule does not apply in regions of strong relief, such 
as the dissected plateau of West Virginia. • When forests 
are cut down, the direct run-off of the rainfall is increased; 
then the springs are likely to run dry and the streams will 
vary greatly in volume between flood and drought. 

Ground water slowly moves from hills and slopes, 
descending to lower levels and accumulating beneath the 
lower ground. It may, therefore, be generally found near 
the surface in valleys, where the soil is usually damp. At 



RIVERS AND VALLEYS 



237 



the base of a slope the ground water m^j issue in a spring, 
-s; Figure 119, supplying a small brook. Innumerable 
small springs occur unnoticed in the banks of streams. 

Ground water stands close to the land surface in marshes, 
swamps, and bogs, rising or falling somewhat with changes 
of weather and season. 

In regions of sufficient rainfall and moderate relief the 
ground water may be reached at almost any point except 
on hilltops by sinking wells to a depth of from ten to forty 




Fig. 119. Section showing Ground Water in Rock Crevices beneath a Valley 

feet. The bottom of the well should be a few feet deeper 
than the level at which the trickling stream of ground 
water enters it, so as to accumulate water in sufficient 
volume to supply ordinary domestic needs. 

Ground water and spring water carry very little rock 
waste (unless in solution) and are generally clear and pure. 
For this reason wells and springs generally afford a better 
water supply than the surface streams that receive the 
wash of fields and meadows. 

In coastal regions ground water may flow forth as springs 
directly into the sea, either on a sloping beach near low-tide 
level, or at the bottom offshore ; here they sometimes have 
a current so abundant as to supply a column of fresh water 
that ascends through the heavier salt water to the surface. 



238 



ELEMENTARY PHYSICAL GEOGRAPHY 



137. Artesian Wells. — In many coastal and interior 
plains a large part of the rainfall enters the more sandy 
la3^ers and follows their gentle slope deep underground, 
between other layers that are less open to the passage of 
water. If a deep well is sunk to the water-bearing stratum, 
the water may rise and flow out of the surface like a foun- 
tain. Wells of this kind are called Artesian, from Artois, 
a district in France where they were first bored. 

It is essential that the water-bearing stratum should 
receive its rainfall at a higher level than that of the top 
of the well by which it is tapped, as shown in Figure 120. 




Fig. 120. Diagram of a Coastal Plain with Artesian Wells 

In what part of the plain does tlie stratum tapped by the deeper 
well reach the surface? 

Charleston, Galveston, and many other coastal cities 
receive much water supply from artesian wells. In east- 
ern Maryland deep wells pierce strata that reach the 
surface and receive rainfall west of Chesapeake bay; the 
strata lead the water beneath the nearly water-tight layers 
that floor the bay, and it is still fresh when rising in the 
wells. Southern Wisconsin and eastern Iowa have many 
artesian wells, supplied by water-bearing strata that slope 
gently away from the older land of northern Wisconsin, 



RIVERS AND VALLEYS 239 

138. Hot and Mineral Springs. — Ground water some- 
times descends deep beneath the surface with a slow supply 
from a large area. While deep underground the water 
acquires a high temperature and stands under a heavy 
pressure. It is shown by experiment that hot water under 
pressure has increased power of dissolving certain minerals. 
Hence the slowly percolating water takes into solution 
Avhat it can dissolve of the more soluble minerals dis- 
covered on its wa}^ such as calcite (the mineral base of 
limestone), salt, and certain compounds of magnesia, iron, 
etc. If the water then rises rather rapidly along a rock 
fracture, it will appear at the surface in springs, bearing 
an unusual amount of mineral substances in solution and 
often having a high temperature. Such springs are fre- 
quently of medicinal value. 

Springs of this kind are associated with disturbed rock 
structures such as occur in mountainous districts. Saratoga 
Springs, N.Y., White Sulphur Springs, W.Va., Vichy in 
central France, and Karlsbad ui Bohemia are examples of 
settlements determined chiefly or wholly by the value of 
their medicinal waters. Many other mineral springs occur 
in the Appalachian and Rocky mountains. 

139. Geysers. — In certain volcanic regions the tempera- 
ture of the underground water may rise to or above the 
boiling point. Steam then issues with the water, often in 
a more or less explosive manner, and such steaming and 
spouting springs are called geysers. The geysers of Ice- 
land have long been famous ; those of the Yellowstone 
Park are now the most celebrated in the world. 



240 



ELEMENTARY PHYSICAL GEOGRAPHY 



The jet of steaming water and spray may rise for several 
minutes to a height of a hundred feet, with a loud roaring 
noise. Then all remains quiet till the next eruption, 
usually a number of hours later. Mineral substances that 

were dissolved in small quantity 
by the hot water underground 
are partly deposited near the 
geyser's vent as the water cools 
or evaporates, and thus a mound 
or terrace of mineral deposits is 
gradually formed. The terraces 
around the hot springs of the 
Yellowstone Park are of great 
beauty. 

The intermittent action of 
many geysers suggests that a 
certain period of time (an hour 
or more) is necessary to warm 
the new supply of water that 
enters the crevice of discharge 
after a previous supply has been 
blown out by steam. Water 
under pressure must be heated 
above the ordinary boiling point 
(212° F.) before it will change to steam. Hence in the 
deeper part of the crevice the temperature of the boiling 
point is higher than at the surface. When the deeper 
water reaches its boiling point a great part of it is quickly 
converted into steam, which blows the rest of the water out 
of the vent. 




Fig. 121. A Geyser 



RIVERS AXD VALLEYS 241 

140. Mud Volcanoes. — Certain hot springs bring a con- 
siderable amount of fine rock waste to the surface with 
their steaming water. The waste is then deposited as a 
muddy sediment around the opening of the spring, where 
it forms a mound with a hollow or crater in the center. 
Although seldom over a few score feet in height, the 
resemblance of these mounds to true volcanoes has given 
them the name of mud volcanoes. A number of mud vol- 
canoes occur in the Yellowstone Park, where some of them 
are only a few feet high. Some of the largest known, 
with heights up to 400 feet, are near the lower course of 
the river Indus in northwest India. 

141. River Systems and their Parts. — A river is a 
stream of water bearing the rainfall and the waste of the 
land from higher to lower ground and, as a rule, to the sea. 
A trunk stream and all the branches that join it constitute 
a river system. 

Stream is a general term, with little relation to size. 
Rill, rivulet, brook, and creek apply to streams of small 
or moderate size. River is generally applied to the trunk 
or to the larger branches of a river system. 

A river flows in a channel that is somewhat lower than 
the adjoining land surface. The floor of the channel is 
the river bed ; the sides of the channel are the liver 
banks. The coarser part of the waste borne by the liver 
is swept along the bed ; the finer part may be carried in 
the stream. 

The land from which a river gathers its water and its load 
of rock waste is called its basin. The crest line, or "height of 



242 



ELEMf:NTARY PHYSICAL GEOGRAPHY 



land," between the basins of neighboring streams or rivers, 
or between the valleys of river branches, is called a divide. 



m\l^u.~~ 



^P:x^ 




Fig. 122. A Divirting Ridge in the Mountains of Northwest England 



Trace the divide shown in Figure 122. Note that a divide may- 
be much higher at one point than at another. Follow some of the 
simple and branching divides shown in Figures 86 and 104. 



RIVERS AND VALLEYS 243 

The land slopes in opposite directions on the two sides 
of a divide. When rain falls on the adjoining slopes it 
will be shed into different streams; hence a divide is 
sometimes called a watershed or water parting. Certain 
crest lines in the Rocky mountains separate the basins of 
rivers which discharge into the Atlantic and the Pacific 
oceans; these crests constitute the "continental divide." 
Name some of the rivers that are thus divided. 

On smooth plains and uplands there is no well-marked 
height of land or ridge separating the headwaters and 
side streams of neighboring rivers. Such surfaces may be 
described as having an undivided or imperfectly divided 
drainage. Undivided drainage areas are often found on 
young plains and plateaus. Compare the foreground and 
background of Figure 62 in this respect. 

When a plain or plateau or mountain region is well 
dissected numerous sharply defined subdivides are devel- 
oped between the smaller rivers and their branches, as 
on the Allegheny plateau. River and stream basins in 
vigorous mountains are sharply divided by the crest lines 
of the lofty ridges between the deeply eroded valleys. A 
worn-down region may have indistinct divides, as on 
the even uplands of the Piedmont belt of Virginia, 
Figure 99. 

Nearly all these features of river systems may be illus- 
trated in a small way by the temporary streams on a road 
surface just after a fall of rain. Many interesting studies 
may be made of the small stream basins, divides, branches 
and channels, and of the manner in which the streams 
bear Avaste from higher to lower ground. 



244 ELEMENTARY PHYSICAL GEOGRAPHY 

142. Floods and Droughts The volume of a river varies 

with the change in the amount of rainfall over its basin. 
Duiing and shortly after a rain (or a thaw of snow) the 
surface run-off is most active ; all the rivulets are running 
with water and waste to the creeks, and the creeks run to 
the rivers. The volume of all the streams is increased at 
such a time, and their current is quickened. The water is 
then turbid with the waste that has been washed into the 
streams by the rivulets on the valley sides and lifted from 
the stream beds by the strengthened currents. As the 
stream volume increases, the water may rise above the 
banks of the channel and overflow the low ground or flood 
plain on either side. There some of the fine river-borne 
waste, or silt, will be deposited as the current slackens. 

When the rain stops and the surface run-off lessens and 
ceases the flooded streams are drained down the valleys 
toward the sea; their volume decreases and their surface sinks 
to a more ordinary level. Then the streams must depend on 
ground water supplied by springs at innumerable points in 
the stream beds. Less waste is washed into. the streams at 
this time, and their current may become nearly or quite clear. 

During a drought of several weeks or months the streams 
drain away much of the ground water. Then the discharge 
of the springs is weakened, and the streams are reduced to 
smaller volume. They may shrink so much as to be unable 
to cover all the bed of their channel, especially in the head- 
water branches. The streams may entirely disappear for a 
time, but even if lost at the surface, ground water may gen- 
erally be found slowly creeping through the sand and gravel 
of the channel bed a few feet below the surface. 



RIVERS AND VALLEYS 245 

In regions of plentiful rainfall, like the eastern United 
States, the rivers may be much reduced during droughts, 
but they do not entirely disappear. In the drier climate 
of many of the Western States the streams habitually dis- 
appear and leave their channels dry during the long inter- 
vals between rain storms. 

143. The Work of Rivers Frequent reference has 

already been made to the work of rivers in sculpturing 
the lands. This important subject may now be con- 
sidered more carefully. The higher a river lies above 
baselevel, the deeper may its valley in time be worn. 
The steeper the channel, the faster the river flows and 
the more and the coarser rock waste it may sweep and 
carry downstream. The greater the volume of a river on 
a given slope, the less it is retarded by friction on the bed 
and banks, and the faster it flows. Hence a river in flood 
floAVS faster than at time of low water, and the flooded 
current transports a greatly increased load of rock waste. 
Indeed, it is chiefly in time of flood that the work of a 
river is performed. 

The deepening of a valley by the erosion of rock in the 
river channel is accomplished chiefly by the rasping of the 
rock surface with the innumerable fragments and particles 
of rock waste that are swept over it. The more resistailt 
the rock, the slower it will be worn down. The particles 
thus worn from the rock surface make part of the load of 
waste borne away by the river. 

As the valley bottom is worn deeper and . deeper below 
the surrounding country, the valley sides are attacked by 



246 ELEMENTARY PHYSICAL GEOGRAPHY 

the weather, and much waste washes and creeps down 
from them into the river, thus widening the valley, 
decreasing the steepness of its side slopes, and adding to 
the load of waste borne away by the stream. It is in this 
sense that it is said that "rivers erode their valleys." 
Another portion of the river load is received from the 
headwaters and side streams, which in turn receive it 
chiefly from the wash of waste down the side slopes of 
their valleys at times of rain or thaw. 

The load of waste thus gathered is not swept along in 
a continuous movement to the sea ; it stops many times on 
the way, being laid down on the bed or sides of the chan- 
nel when the water is low, forming bars and banks ; it is 
swept forward again a greater or less distance at time of 
flood. 

Rivers that are beginning their work of erosion and 
transportation in sculpturing a newly uplifted land may be 
called young. When they have worked so long that all 
the land slopes in their basin have been worn down low, 
so as to form a surface of faint relief — a peneplain — at 
a small altitude above sea level, the rivers may be called 
old. Between youth and old age, when the rivers are 
actively working in well-carved valleys, sweeping along 
the waste received from the hills or mountains that form 
the valley sides, they may be called middle-aged or mature. 

144. Young Rivers. — The examples of land forms 
described in earlier chapters have shown that when a 
region is first raised from the sea, or when a former 
land surface is uplifted, tilted, or folded, the streams as 



RIVERS AND VALLEYS 247 

a rule follow the lead of the land slopes, uniting here 
and there to form rivers of larger and larger size. 

Young rivers thus newly established proceed to cut 
down their channels where the slope is steep enough to 
give them an active current; the waste that they gather 
is washed along, rasping down the ledges in the river 
bed; but where the slope is very faint, or where rivers 
enter a basin holding a lake, they lay down their load 
of waste and build up the land surface. 

While rivers are still young their course is often 
marked by rapids and falls, not yet eroded away, and 
by lakes not yet filled up with sediments or drained 
away by the deepening of their outlet by the outflowing 
stream. The current of such rivers is irregular, being- 
very fast at rapids and falls and almost wanting in lakes. 
As the river grows older both the falls and the lakes dis- 
appear and the current becomes more uniform. 

The drainage of the Laurentian highlands of Canada 
north of the St. Lawrence river bears every mark of youth. 
Lakes are very numerous and of irregular form. They 
often have several outlets, no one stream having cut 
down enough faster than the others to secure all the 
discharge. The streams are frequently interrupted by 
rapids or fslls on rock ledges, in which channels are as 
yet cut only to moderate depth. The rivers frequently 
split into two or more channels, which reunite after wan- 
dering in independent courses for ten or twenty miles 
across country. 

These highlands are a rugged, forested, and thinly popu- 
lated wilderness without roads. All travel is by canoes 



248 



ELEMENTARY PHYSICAL GEOGRAPHY 



along the water courses, and the canoes have to be car- 
ried past every rapid and fall. The birch tree, from whose 
bark portable canoes are made, is here as appropriate to 
the needs of the inhabitants as the camel is to the dwellers 
in arid deserts. 

The St. Lawrence system, with its many lakes, falls, 
and rapids, is a remarkable example of very young or 




Fig. 123. Niagara Falls 



undeveloped drainage. The outlet of Lake Superior is 
by a river interrupted by rapids, called the Sault Sainte 
Marie (Soo St. Mary). The outlet of Lake Erie is 
Niagara, with its renowned cataract and rapids. The out- 
let of Lake Ontario is the St. Lawrence, with numer- 
ous rapids. The lakes favor navigation, but the rapids 
and falls obstruct it. Canals and locks have now been 



RIVERS AND VALLEYS 249 

constructed, by which the rapids and falls are passed. 
Name the great lakes of the St. Lawrence system. 

The region of the great African lakes bears many marks 
of youthful drainage. The lake basins here indicate a break- 
ing or warping of the earth's crust, like that in southern 
Oregon. The inclosing plateaus are bordered by ragged 
cliffs, where fractures have taken place. The Nile, flowing 
north from Lake Victoria Nyanza, and the Shire, flowing 
south from Lake Nyassa, are young rivers of powerful cur- 
rent, descending over falls and rapids, and are very busy in 
the work of deepening their valleys and draining the lakes. 

By long-continued action the path of a river will in 
time be everywhere worn down or built up to such a 
slope that the current will be just strong enough to 
carry the load of waste that it receives. Such a river 
may be described as passing from youth to maturity. 

145. Lakes may be generally taken to indicate a youth- 
ful drainage system, as in the examples just given. In 
time they will be destroyed, partly by filling with the 
waste that is brought by the inflowing streams, partly 
by the deepening of the outlet valley. Lakes should 
therefore be regarded as only temporary features in the 
long life of the river system to which they belong. The 
rivers may remain long after the lakes disappear. 

The depressions between the tilted lava blocks of south- 
ern Oregon hold lakes because enough time has not yet 
passed to enable the streams to fill and drain their basins. 
Lava flows obstruct streams and for a time hold back 
lakes. Lakes of other kinds will be described IS/tQw 



250 ELEMENTARY PHYSICAL GEOGRAPHY 

As the current of a river decreases on entering a lake, 
the stream-borne waste settles ; thus deltas are formed at 
the inlets and the lake bottom is strewn with the finest 
waste or silt. 

Lake Geneva in Switzerland receives the Rhone at its 
east end ; the river is turbid with the waste that it has 
received from Alpine glaciers and torrents. A delta 
twenty miles long has been built into the lake. It has 
grown a mile forward since Roman times, nearly 2000 
years ago. The lake bottom is a plain of fine silt. When 
even the finest silt has settled, the lake water becomes 
very clear, and the Rhone at the outlet is wonderfully 
transparent. 

Lakes act as regulators of the discharge of their 
outflowing rivers ; for the level of the lake changes 
little, whether the inflowing streams are flooded or 
low, and hence the outlet river has a relatively constant 
volume. 

The Ohio without lakes and the St. Lawrence with five 
great lakes are strongly contrasted in respect to floods. 
The latter has no great floods, because even a heavy 
rain raises the surface of the lakes gradually and only 
by a small amount ; hence the outflowing river cannot 
be greatly increased in volume. The rains of the upper 
Ohio basin, a hilly district, are not detained in lakes, but 
quickly flow down the hillsides to the streams. Floods 
in the Ohio valley may rise fifty or sixty feet in a few 
days, spreading to ten or twenty times the usual width 
of the river and causing great damage to villages and 
cities on the valley floor. 



RIVERS AND VALLEYS 



251 



146. Falls and Rapids. — When a river begins to 
wear its valley it rushes down any descending slope 
that occurs on its course. Here a gorge is cut as the 
rocks are rasped away by the gravel and sand in tlie 
rapid current. Niagara, when first taking its present 
course, fell over the north-facing bluff of the upland 




Fig. 124. Diagram of Niaaara River between Lakes Erie and Ontario 



that separates the basin of Lake Erie from that of Lake 
Ontario ; since then the river has cut back a gorge about 
seven miles long from the edge of the upland ; the falls 
now plunge into the head of the gorge. The larger or 
Canadian fall is now retreating three or more feet a year 
at its middle. 

The falls of the Yellowstone river occur at the head of 
a deep canyon cut by the river in the process of deepening 



252 



ELEMENTARY PHYSICAL GEOGRAPHY 



its course through a lava plateau. As the falls are worn 
back the gorge is lengthened. 

While a stream is engaged in deepening its valley it 
often flows from a harder to a softer rock structure. It 
will deepen the valley much more quickly in the latter 
than in the former, and a rapid or fall will be formed on 




Fig. 125. Falls of the Yellowstone River 



the abrupt slope between the two. Falls and rapids of 
this kind are numerous, especially in dissected plateaus 
and mountains. 

.It has long been the custom to build mills near falls, so 
that part or all of the descending water may be used to 
turn water wheels and thus to drive the machinery of the 
mills. Villages have often grown up around the mills 
and factories thus located. As the work of the mills 
increases it has frequently been necessary to add steam 



RIVERS AND VALLEYS 



253 



power to water power ; at the same time the village may 
grow to be a large city. In recent years it has been found 
possible to transform the power of falling water into an 
electric current, which may be carried many miles through 




Fig. 120. Diagram of Torrent, with Falls and Reaches 

How many falls are shown in Figure 126? Draw a profile along 
the river course and compare its slope at and between the falls. 
AVhy are some of the stretches between the falls longer than others ? 
Where are the gorges deepest ? 

wires and then set to work to drive machinery, to run 
cars, or to furnish electric light. Waterfalls in thinly 
populated mountains may thus in time come to be used to 
supply electric power to cities on the neighboring plains. 



254 ELEMENTARY PHYSICAL GEOGRAPHY 

147. Graded Rivers. — A river cannot wear down its 
course to a level, for there must be some slope down 
which the current, bearing its load of rock waste, may 
flow toward its mouth. While the slope is strong and 
the current is very swift the stream is called a torrent. 
The waste is then swept along so actively that bare rock 
is commonly seen in the stream bed. Torrential streams 
are usually clear, because they quickly sweep away the 
fine particles that they receive from time to time, leaving 
coarse cobbles and bowlders lying on their rocky channels. 
Such streams are still young. 

As time passes and the channel is eroded deeper and 
deeper it will be worn down more nearly level, closer and 
closer to baselevel. But it must always preserve a slope 
sufficient to give the water a velocity that will enable it 
to wash forward the load of waste received from the head- 
waters and side streams, though without either deepening 
or building up the bed of the channel significantly. When 
such a slope is attained the river is said to be graded. It 
has reached maturity. 

The current of a graded river is usually deliberate 
instead of torrential. Its bed and banks consist, for the 
most part, of deposits of rock waste ; firm ledges are seldom 
seen along its course. The water is usually made some- 
what turbid or muddy by the presence of fine waste, with 
which it is plentifully supplied by its tributaries and by 
the wash from its bed and banks. 

In valleys among high mountains, where an abundant 
supply of coarse waste is washed down from the steep 
valley sides, graded streams must have a slope strong 



RIVERS AND VALLEYS 255 

enough to give them an active current ; otherwise their 
coarse and abundant load could not be washed forward. 
In lowlands where only fine-textured waste of the land is 
slowly washed into the streams, graded rivers have a very 
gentle descent. 

Water moves so easily that large rivers assume very 
faint slopes; the lower Mississippi has a descent of only 
two or three inches to the mile, yet it bears along a vast 
amount of rock waste, — 6700 million cubic feet of sus- 
pended silt, 750 million of silt dragged along the bottom, 
and 1400 million of minerals in solution every year. 

148. Reaches and Rapids. — A longer time is required 
to wear a valley down to grade where the rocks are resist- 
ant than where they are weak. If a river crosses a suc^ 
cession of weak and strong rocks, as in Figure 126, the 
graded condition will be first attained on the weak rocks, 
and each reach of the river on the weak rocks will be 
graded with reference to the sill of hard rocks next down- 
stream or with reference to the lake or sea into which the 
river may flow. The sills of hard rocks then serve as local 
baselevels with respect to which the stretch or reach next 
upstream is graded. 

Manj^ rivers come in this way to be divided into long 
smooth reaches and short plunging rapids or falls. Most 
of the rivers of New England and of eastern Canada are 
in this condition. 

When a river system has been undisturbed for a long 
period of time, even the resistant rocks are worn down. 
Few falls then remain to interrupt the steady flow of the 



256 ELEMENTARY PHYSICAL GEOGRAPHY 

river current, and its graded reaches become longer and 
longer. The side streams, following the example of the 
master stream, wear down the side valleys so as to join the 
main valley at even grade. It is in this well-established 
condition that many large rivers of the world are found. 
When a graded condition is reached in even the smaller 
branches of a river system the slope will be steepest in 
the headwater streams and least near the river mouth; 
thus the profile of a well-developed river is a curve of 
decreasing slope from head to mouth. 

149. The Development of Valleys. — While a young river 
is deepening its valley, the valley sides are steep and the 
valley bottom is no wider than the river channel, as in Fig- 
ure 127. At such a time the valley floor offers no attraction 
to settlement, as it affords no level ground for roads near 
the river ; roads built in such a valley must perch on the 
side slope. If the valley is deep, like the Colorado canyon, 
it may act as a barrier between the uplands on either side. 

Floods have little room to spread in a steep-sided valley ; 
hence they rise rapidly on the valley walls, even thirty 
feet or more in a day or two. Thus confined in the valley, 
the flood flows rapidly and sweeps away all obstacles, 
gradually subsiding as its supply of water lessens. 

It is for this reason difficult to maintain road bridges 
across the streams of the Allegheny plateau. Figure 79; 
the great expense of building strong and high bridges can- 
not be borne by the scattered population. The streams 
are therefore commonly crossed by fording. At time of 
high water travel is interrupted. 



RIVERS AND VALLEYS 



257 



The continued action of the river, wearing first on 
one bank and then on the other, gradually widens the 
valley floor. At the same time the sides of the valley are 




Fig. 127. Valley of Yakima River, Washington 

worn back to gentler slopes, and the valley floor becomes 
more accessible. 

At this stage of development the valley is mucli more 
available for human uses than when young, narrow, and 



258 



ELEMENTARY PHYSICAL GEOGRAPHY 



steep-walled. Villages may be built and fields may be 
cultivated on the valley floor. Roads may follow it on 
each side of the river. Instead of being a trenchlike bar- 
rier between two highlands, the valley has now become a 
well-graded pathway for settlement and for trade between 
the upper and lower parts of the river system to which it 




Fig. 128. The Mohawk Valley 



belongs. The Mohawk valley in eastern New York, Fig- 
ure 128, is a good example of this kind. Another is 
shown in Plate X. 

The behavior of rivers during the advance in the devel- 
opment of their valleys must now be considered in greater 
detail. 

150. The Development of Flood Plains. — In a winding 
stream the fastest current is displaced from the middle 
of the channel toward the outer bank. Such a stream 



RIVERS AND VALLEYS 



259 



therefore tends to cut more on the outer bank than on 
the inner bank at every turn ; hence as it cuts down it 
also cuts sideways. 

When grade is reached the valley walls will be slant- 
ing, but they will be steepest on the outer side of every 
bend, where the stream has undercut the valley wall, as in 
Figure 129. The valley walls will therefore be equally 
steep on the two sides only where the valley is straight. 
At each turn sloping spurs descend opposite abrupt cliffs, 
and the belt of country occu- 
pied by the turns of the river 
is broadet than at first. 

Draw a map of the district shown 
in Figure 130 a, following the style 
of Figure 129, and show where the 
river is undercutting the cliffs. 
The river is supposed to be flowing 
toward the front of the diagram 
in Figure 130. 

Fig. 120. Outline Map of a 

When a river has worn down Young Valley 

its valley to a gentle slope it 

still wears on the outer bank of every turn, because the 
strong 'current runs there; thus the valley floor is broad- 
ened. At the same time the turns tend to become smooth 
curves of regular form. 

As the outer bank of a curving channel is slowly cut away, 
the inner bank, where the current runs slower, is gradually 
filled up nearly to high- water level with rock waste from 
farther upstream. A curved strip of fiat valley floor is 
thus developed on the inner side of each curve, as in 




260 



ELEMENTARY PHYSICAL GEOGRAPHY 



Figure 130 h, first on one side and then on the other side of the 

river. As the valley floor 
is exposed to overflow at 
times of flood, the flat 
land bordering the stream 
is called the flood plain. 

Draw a map of the district 
in Figure 130 J. Describe the 
shape and position of the 
patches of flood plain. What 
difficulties would be met in 
making a road along the val- 
ley bottom ? 

With continued action 
the river consumes more 
and more of the spurs that 
enter its curved course, as 
in Figure 130 c, d. In 
time the spurs are all worn 
away, as in Figure 130 e. 
Then an open flood plain 
is formed on which the 
river freely follows such a 
curved course as best suits 
its volume. With still fur- 
ther action of the river the 
flood plain will be slowly 
Fig. 130. Diagrams of a Widening Valley widenedto greater breadth. 

The valley will then be more attractive to settlement than 
before, with room for villages and fields on its floor. 




RIVERS AND VALLEYS 261 

Which side (up-valley or down- valley) of the middle spur in 
Figure 130 c has been worn away? Draw a map representing 
Figure 130 d. 

Describe the form of the upland in the diagrams of Figure 130. 
Compare the form and breadth of the flood plain in the different 
diagrams. Compare the slopes of the valley sides. Compare the 
forms of the upland spurs that enter the curves of the valley. 

When a river overflows, the greatest amount of silt 
is laid down on the flood plain near the river channel. 
Thus in time the plain comes to have a gentle slope 
away from the river on either side, as well as down the 
valley. 

If a stream has a large load of coarse rock waste, its 
graded flood plain must be relatively steep (a descent of 
from five to twenty feet or more in a mile). In this case 
the stream does not turn far aside from a direct course 
along the flood plain to form serpentine curves; but it 
is constantly embarrassed by the formation of bars and 
islands of gravel and sand, splitting its current into a 
braided network of channels. 

The Platte is a river of this kind. It gathers much 
waste from the weaker rocks of the Great plains and 
therefore requires a rather strong slope for its graded 
valley floor. Many rivers flowing from the Alps to the 
lower lands have gravel bars and islands between their 
braided channels, as in Plate XL 

151. River Meanders. — If the waste borne by a river 
is of very fine texture, the flood plain will have a very 
gentle grade. Then the river easily turns aside from a 
direct course on its broadened flood plain, and in this 



262 



ELEMENTARY PHYSICAL GEOGRAPHY 



way (whatever its original path) deveh)ps a system of 
serpentine curves, as in Figure ISO d,e. Curves of this 
kind are called meanders, after the Meander, a winding 
river of Asia Minor. How many turns does the river 
make in Figure 131? 

The size of the meanders increases with the volume of 
the stream. A meadow brook may swing around curves 




Fig. 131. A Meandering River, Vale of Kashmir, India 

measuring only forty or fifty feet across. The curves of 
the lower Mississippi are from three to six miles across. 
The flatter the flood plain, the greater is the meander turn- 
ing. The Koros, Figure 132, on the Plain of Hungary, 
has its meanders remarkably developed. 

Meanders are slowly changed, for the river wears away 
the outer bank of each curve because the current runs 
fastest there ; the opposite side of the channel is filled 



RIVERS AND VALLEYS 



263 



in with waste where the current is slow. The Mississippi 
below Cairo has in the course of ages shifted its course, 
now eastward, now westward, an'd has thus opened a flood 
plain from twenty to sixty miles wide, that is, five or six 
times wider than its meander belt. Similar changes may 
be seen on a small scale in a meadow brook. 

In the fine silt of a broad and flat flood plain a large river 
changes its course easily and rapidly; it takes material 
from the outer bank, 
where its current is 
strong, and deposits it 
farther downstream 
on the inner bank, 
where the current is 
weaker. 

The necks of the 
flood-plain spurs be- 
tween adjoining 
meanders are often 
gradually narrowed 

and cut through by the river, the meander around the 
spur being then deserted for a shorter and more direct 
course, called a cut-off. Where are cut-offs likely to 
occur in Figure 132? 

Large rivers, like the Mississippi, exhibit all stages 
of this process. An abandoned meander is occupied 
by nearly stagnant water, more or less completely sep- 
arated from the new and shorter channel by deposits 
of silt in the ends of its arms ; in time it becomes an 
oxbow lake. 




Fig. 132. A Meandering River on the 
Plain of Hungary 



264 



ELEMENTARY PHYSICAL GEOGRAPHY 



Draw an outline map to show the probable path of the Mississippi 
when it ran through the oxbow lakes, Figure 133. How does the 
channel of 1896 differ from that of 1882 ? 

The shifting of the channel may be checked by pro- 
tecting the outer bank 
with stone or wood, 
but this is expensive. 
Rising floods may be 
held back by dikes or 
levees built on the 
plain a little distance 
from the river banks. 
When the levees are 
overtopped or breached 
widespread floods may 
result, such as occurred 
on the Mississippi flood 
plain in April, 1897, 
when about 13,000 
square miles of the 
plain (two fifths of the 
entire area) were under 

Fig. 133. Meandering Channel and Oxbow ^yater. The Value of 
Lakes in the Flood Phiin of the Mississippi, , 

according to Surveys in 1882 and 1883. The ll"^® stock and CropS 

position of the channel according to surveys lost in this flood was 
in 1895 and 1896 is shown by dotted lines. ,. , , , m.i i- nnn 

estimated at ^15,000,- 
000 ; many thousands of people were for a time driven 
from their homes. 

In March, 1890, a strong flood in the lower Mississippi 
broke through the levees on the left bank, forming the 




RIA^ERS AND VALLEYS 265 

" Nita crevasse " (a break on the Nita plantation), flood- 
ing the plain, carrying river silt into the shallow waters of 
the Gulf of Mexico, and ruining the oyster beds east of 
the delta. 

152. Alluvial Fans of Large Rivers. — When rivers flow 
from mountains or plateaus and enter open lowlands, 
where no valley walls inclose them, they may build exten- 
sive alluvial fans of faint slope. The Merced river of 
California (see M, Figure 134) offers a good illustration 
of this habit. 

The Merced gathers much waste from its steep head- 
waters in the Sierra Nevada. On issuing from its narrow 
valley at the mountain base it is free to run in any direc- 
tion — forward, to the right or to the left — on the broad 
" valley of California," a belt of low country between the 
Sierra and the Coast range. Here the river, flowing first 
in one direction, then in another, has built a fan about 
forty miles in radius, of gravel near the mountains, of fine 
silt farther forward. 

As the rain of this region falls chiefly in winter, it is 
necess'ary to irrigate the fields for summer crops. Nothing 
could be better adapted to the needs of irrigation than a 
gently sloping alluvial fan; for the river may be easily 
turned into various channels at the head of the fan and 
led forward on different courses, and thus distributed over 
thousands of acres. 

One of the largest alluvial fans in the world is that of 
the Hoang-Ho, in eastern China. This great river, bear- 
ing a heavy load of fine silt from the basins among the 



266 



ELEMEJiTTARY PHYSICAL GEOGRAPHY 



inner mountains, issues from its inclosed valley 300 miles 
inland from the present shore line, and at a height of about 
400 feet above sea level, and then flows to the sea down 
the gentle slope of its extensive fan. 

The great fan of the Hoang-Ho 
is very fertile and supports one 
of the densest populations on the 
earth ; but it is subject to overflow 
on a vast scale, when the river 
suddenly changes its course from 
one path to another and invades 
fields and villages on a new course 
to the sea. Overflow is prevented 
as far as possible by dikes; but 
the channel has repeatedly been 
changed during the many cen- 
turies of Chinese history. 

The loss of life caused by these 
overflows is very great. Not only 
are many thousands of people 
drowned, but the crops are de- 
stroyed over large districts, caus- 

T, .o. m, ,r ,1 . ins: famines in which many more 
Fig. 134. The Valley of ^ , -^ 

California thousands perish. 




153. Broad Plains formed by Rivers. — When many 
rivers flow forth from mountain valleys upon a neighboring 
lowland their adjoining fans unite in a broad plain slop- 
ing gently forward from the mountain base. This may be 
called a river-made plain. It resembles a coastal plain in 



RIVERS AXD VALLEYS 



267 



having higher land for a background, but it does not neces- 
sarily front upon the sea, and it is generally but little 
trenched by the rivers that built it. A plain of this kind 
often occupies the depression between two highlands or 
mountain ranges. 

The many rivers issuing from the valleys of the Sierra 
Nevada and the 
Coast range upon 
the "valley of Cali- 
fornia" have formed 
an extensive plain, 
of which the Mer- 
ced fan, described 
above, is only a part. 
The successive fans 
are very broad and 
flat, so that their 
slightly convex form 
can hardly be seen. 
The fans from the 
east and west meet 
in a flat-floored 
trough, Figure 134. 




Fig. 135. 



Torrent Fan Delta, Lake Geneva, 
Switzerland 



154. Deltas. — When a river enters a lake or the sea its 
current is checked. The finest part of the waste may be 
swept away by waves and tides ; the rest accumulates at 
the river mouth and builds up a new land surface, called a 
delta, in advance of the original shore line. The fans of 
mountain torrents form deltas in lakes at the mountain 



268 



ELEMENTARY PHYSICAL GEOGRAPHY 



base. Small deltas are characteristic of young rivers ; the 
longer the progress of river growth, the larger the delta 
may become. 

The land surface of a delta is built on the same slope 
as that of the river flood plain farther upstream, the delta 
being only the forward part of the flood plain. Under 
water a delta slopes at a steeper angle than above water. 

The great fan of 
the Hoang-Ho may be 
regarded as its delta, 
because it has been 
built forward into the 
Yellow sea (so named 
from the color given 
by the river waste). 

A river frequently 
splits into several 
channels on its delta, 
the outgoing branches 
being known as dis- 
tributaries. These are well exhibited in the fingerlike 
divisions of the Mississippi on its outer delta. Figure 136, 
and in the many channels of the Ganges and the Brahma- 
putra on their deltas at the head of the Bay of Bengal. 
How many distributaries are shown in Figure 136 ? 

Great rivers may build their deltas in the face of waves 
and tides. At the Mackenzie delta the tidal range is three 
feet, at the Niger four feet, at the Hoang-Ho eight feet, 
at the Ganges-Brahmaputra eighteen feet. The building 
of deltas by small rivers is favored by the protection from 




SOUTH PASS 



g SOUTSWEST PASS 



Fig. 13G. The Delta of the Mississippi 



RIVERS AND VALLEYS 269 

waves in bay heads and by the weakness or absence of 
tides. Where are the above-named rivers ? 

The absence of deltas at the embayed mouths of certain 
rivers is frequently not so much because the tidal currents 
sweep away all the river silt, as because there has not yet 
been time enough to build a delta since the embayments 
were formed by the depression of the coastal lands. 

The lower valleys of the Delaware, Susquehanna, Poto- 
mac and neighboring rivers are drowned, forming bays in 
the partly submerged coastal plain of the Middle Atlantic 
States. Whatever deltas these rivers previously built are 
now beneath the sea. Very little delta growth has yet 
taken place at the bay heads ; hence the depression of the 
region is relatively recent. 

The deltas of large rivers consist of fine-textured waste 
or silt, worn during the long journey from the river head- 
waters and weatliered during many rests in the flood plain 
on the way. In a favorable climate deltas are very fertile 
and attract a large population. The three densest popula- 
tions of the world (outside of large cities) are in eastern 
China, northeastern India, and northern Italy, all on the 
lower flood plains and deltas of large rivers. 

« 155. Mature Rivers. — When a river and its larger 
branches have destroyed their lakes and falls and reduced 
their valleys to graded slopes, when all the side valleys 
join the larger valleys at grade, when the larger streams 
have broadened their valley floors so that they can meander 
freely upon flood plains in curves appropriate to their 
volume, and when a delta is built forward at the river 



270 ELEMENTARY PHYSICAL GEOGRAPHY 

mouth, the river system has reached the mature or full- 
grown stage of its development. 

Mature rivers accomplish the drainage of their basins 
and the carrying of rock waste to the sea in the most per- 
fect manner. No undivided uplands remain from which a 
great part of the rainfall may be returned to the atmos- 
phere by evaporation. The largest possible share of the 
rainfall is shed from the well-carved surface of the land 
and runs off in the streams with no delay in lakes or haste 
in falls. No hard rock ledges remain to be worn down in 
the valley floors. Everywhere the waste of the land is 
washed down the slopes to the streams and delivered in 
such quantity that the streams are kept working at their 
full capacity to transport the waste toward the sea. 

The valleys of mature rivers are easily followed by roads 
and railroads ; they are broad enough to contain cultivated 
fields as well as villages and cities, as in Plate X. 

156. Old Rivers. — If no disturbance occurs, a maturely 
developed river system passes by slow degrees into a quiet 
old age. The hills waste away to fainter slopes and yield 
less and less waste to the streams. The texture of the 
waste becomes finer and finer. More of the waste is car- 
ried in solution. 

The extreme old age of a river system would be char- 
acterized by low and ill-defined divides between faint slopes 
leading to broad flood plains, on which the streams would 
meander with great freedom. An increasing share of the 
transported waste would be dissolved. A large amount of 
rainfall might be lost by evaporation on the gentle slopes. 



RIVERS AND VALLEYS 271 

It is unusual to find an old river system. The lower 
trunks of large river systems often gain very gentle slopes 
and free-swinging meanders, but before old age is attained 
by all the small side branches and the headwaters move- 
ments of elevation or depression generall}^ occur in the 
earth's crust, with more or less tilting and breaking ; and 
in this way the rivers are made young again and set to 
work at new tasks. 

157. Revived Rivers. — At any stage in the erosion of 
a region drained by a river, the river basin may be uplifted 
to a greater height above sea level. Then the river will 
at once begin to cut its valley floor deeper than it could 
have done before. Such rivers may be called revived. 

Old rivers flowing across low worn-down mountains are 
rare, but revived rivers flowing through gorges in uplifted 
lowlands of this kind are common. The rivers and their 
narrow valleys in the Piedmont district of Virginia are 
thus explained. 

If a meandering river is revived, it will intrench itself 
beneath its former flood plain ; then its new valley will be 
regularly curved after the pattern of its meanders. 

The north branch of the Susquehanna follows a deep 
and winding valley of this kind through the Allegheny 
plateau of northern Pennsylvania. The Osage has an 
extremely serpentine valley in the uplands of central Mis- 
souri. Both these rivers seem to have learned to meander 
when the uplands were lowlands. Since these regions 
were raised the rivers have cut down valleys of a meander- 
ing pattern. The valleys are still narrow. The rivers are 



272 



ELEMENTARY PHYSICAL GEOGRAPHY 



enlarging their curves by cutting away the outer bank; 
here the river is bordered by steep bluffs. Strips of flood 
plain are beginning to form on the inside of the river 

curves where the banks 
are low and flat. 



Draw a map of the district 
shown in Figure 137. Describe 
the form and arrangement of 
the patches of flood plain. 
AMiere are the valley sides 
steep ? Where are their slopes 
gentler ? 




Fig. 137. Diagram of a Narrowed Spur 
in a Meauderiug Valley 



It sometimes happens that a revived meandering river, 
eroding its outer bank, may wear through the neck of the 
naiTowest upland spurs that enter its trenched course ; it 
will then desert a round- 
about course for a more 
direct one, Figures 137, 
138. Rapids will occur 
for a time at the cut-off. 




Draw two maps of the dis- 
trict shown in Figure 138, one 
showing the path of the river Fig. ir>8. 
just before the cut-off was 
made, one just afterwards. 
Compare the first of these maps with the one drawn from Figure 137. 



Diagram of Cut-Olf Spur in a 
Meandering Valley 



The village of Lauffen (Rapids) on the river Neckar in 
southern Germany gains water power from rajiids formed 
at a recent cutroff. The former course of the river is seen 
in a meadow beautifully curved around an isolated hill, 



RIVERS AND VALLEYS 



the cut-off end of an upland spur, Figure 139. 
cut-off spur is seen near the village of Hofen. 



273 
Another 



158. Water Gaps. — Many rivers cross the hard-rock 
ridges of the Allegheny- 
mountains of Pennsyl- 
vania in sharp notches, 
called water gaps. For 
example, the Delaware 
river gathers many 
branches from the open 
valleys of northeastern 
Pennsylvania and es- 
capes by a deep, narrow 
notch, called the Dela- 
ware Avater gap, in Kitta- 
tinny mountain, at the 
northwestern corner of 
New Jersey. 

Such cases are ex- 
plained as follows. Once 
the whole region stood 
lower than noAV and a 
lowland spread far and 
wide at about the level of what are the ridge crests to-day. 

With the elevation of the region all the revived rivers 
begin to wear down their valleys. Where a trunk river cuts 
down its new valley across the belt of hard rock that is to 
make the mountain ridge, the valley remains narrow for a 
very long time ; but elsewhere the valleys of the trunk and 




Fig. 139. 



Intrenched Meanders of 
the Neckar 



274 



elp:mentary physical geography 




Fig. 140. Transverse and Longitudinal Streams 



branch streams widen 
rapidly in the weaker 
rocks, and in time all 
the hills of the weak- 
rock belts are worn 
away, leaving a low- 
land on each side of 
the hard-rock ridge, 
through which the 
water gap has been 
cut, as in Figure 141. 
This explanation 
applies to the Susque- 
hanna, cutting gaps in 
the Allegheny ridges, 
Figure 142, and to 
the stream that has cut a deep passage in one of the Alle- 
gheny ridges in Maryland, shown in Plate IX. 




Fig. 141. TransTerse and Longitudinal Valleys 




Fig. 142. Water Gap of the Susquehanna above Harrisburg, Peunsylvania 

Where must one stand in Figure lil to gain a view like that 
of Figure 142? How many water gaps are shown in Figure 103? 



RIVERS AND VALLEYS 275 

QUESTIONS 

Sec. 134. How is the rainfall of a region disposed of ? What is 
ground water ? Under what conditions will much of the rainfall be 
evaporated into the air? discharged by streams? absorbed by the 
ground ? What is the run-oif ? Of what value is gi-ound water ? 

135. How are caverns generally formed? What is a sink hole? 
What effect have sink holes on surface streams ? Describe an under- 
ground stream. Describe the animals of caverns. What is the 
origin of the Natural bridge of Virginia? 

136. What is a spring? Upon what does the variation of stream 
volume depend? Under what conditions is the variation small? 
Describe the movement of ground water. Where is it found at a 
small depth ? To what depth should wells be dug or bored ? Why 
is spring water purer than stream water ? 

137. What is an Artesian well ? How is its water supplied ? Name 
some districts where such wells are common. What is the relation 
of certain Artesian wells in eastern jNfaryland to Chesapeake bay? 

138. Explain hot springs. Why are they commonly charged with 
mineral salts ? Of what value are they ? Name some examples. 

139. 140. What is a geyser? Where are the most famous gey- 
sers ? Describe and explain the action of geysers ; of mud volcanoes. 

141. Define river, river system, river basin, divide, channel, bed, 
banks. What is meant by a continental divide? by undivided 
drainage? by subdivides? What features of a river system have 
you seen illustrated in a small way? 

142. Describe a river flood. Where is the river-borne waste 
laid down ? How is a river supplied after a flood subsides ? How 
does a drought affect ground water? springs? streams? Compare 
the streams of the rainy and of the drier parts of the United States. 

143. GiA'e some examples of the work of rivers from earlier chap- 
ters. Upon what does the depth to which a valley may be cut 
depend? How do slope and volume affect the velocity of a stream 
and its load of sediment ? Why does a river carry more sediment at 



276 ELEMENTARY PHYSICAL GEOGRAPHY 

time of flood ? How is erosion performed by rivers ? What is the 
source of tlie rock waste borue by rivers V In what sense is it said 
that "rivers erode their valleys"? Under what conditions may a 
river be called young? old? mature? 

144. How is the course of a young river determined? What 
work is done by young rivers ? What are the characteristics of 
young rivers? Describe the St. Lawrence system; the drainage of 
the Laurentian highlands ; that of the region of the great African 
lakes. What changes occur as a river passes from youth to maturity ? 

145. How are lakes converted into rivers? Illustrate by Lake 
Geneva. In what part of the life of a river system are lakes most 
common ? How do lakes affect the transparency and the steadiness 
of flow of their outflowing streams? Compare the Ohio and the 
St. Lawrence as to floods. 

146. Where are falls and rapids formed in young rivers ? How are 
gorges formed ? Illustrate by the gorge of the Niagara ; by the Yel- 
lowstone canyon. How do differences in rock structure determine 
the 'occurrence of falls or rapids ? What uses are made of waterfalls ? 

147. Describe a torrent. What determines the least slope to 
which a river can wear down its course ? Describe a graded river. 
Where have gi'aded streams a relatively strong slope? Why? 
Where have they a very faint slope ? Why ? State the slope and 
the load of the lower Mississippi. 

148. Where are graded reaches first developed in a river ? "Where 
do rapids siu'vive longest? What is a local baselevel? In what 
condition are the rivers of New England? What other region has 
similar rivers? Describe a river that has long been undisturbed. 
Describe the stream slopes in a well-graded river system. How do 
its branches join its trunk? AVhy are they thus related? 

149. Describe the valley -of a young river. What disadvantages 
does it present to occupation? How do floods act in such valleys? 
Illustrate from the Allegheny plateau. How is a valley floor wid- 
ened ? What changes do the valley sides suffer ? What advantages 
are presented by a widened vaUey ? 



RIVERS AXD VALLEYS -277 

150. Describe the action of a winding stream. Describe its val- 
ley when grade is reached. What changes occur after grade is 
reached ? Compare the outer and inner sides of river curves. Where 
and in what pattern is the flood plain first developed ? Describe the 
later changes in the valley spurs ; in the flood plain. Where is the 
most silt laid down during a flood ? How does this affect the form 
of a flood plain ? How does a heavy load of waste affect the behavior 
of a river ? Give an example. 

151. How does a light load affect the course of a river and the 
slope of its flood plain ? What are meanders ? What is the deriva- 
tion of this term? On what does the size of meanders depend? 
How does their form vary ? How has the cou.rse of the Mississippi 
changed? How have these changes affected its flood plain? What 
is an oxbow lake ? Describe an example. How is the shifting of a 
river channel checked ? How are flooded rivers restrained ? Describe 
the effects of the Mississippi flood of 1897. Describe the Nita crevasse. 

152. 153. Describe the fan of the Merced river. Why is irriga- 
tion needed here? How -is it favored? Describe the fan of the 
Hoang-Ho, and its relation to the people of China. Describe a river- 
made plain. Give an illustration from California. . 

154. How are deltas formed ? W^hat is the relation of a delta to 
a flood plain ? What are distributaries ? Describe some examples. 
What is the relation of deltas to tides ? Give examples. Why are 
deltas wanting at certain river mouths ? Give examples. What is 
the relation of large deltas to population ? 

155, 156. What are the features of mature rivers ? Describe the 
work of mature rivers ; the change from a mature to an old river ; 
an old river system.^ Why is it unusual to find old rivers? 

157. What is a revived river ? Describe the rivers of the Pied- 
mont belt in Virginia. Describe the valley of a revived meandering 
river. Give two examples. What changes may happen in such 
valleys? Illustrate by the Neckar. 

158. What is a water gap ? Give an example. Explain it. What 
is the origin of the lowland upstream from a water gap ? 



CHAPTER IX 
DESERTS AND GLACIERS 

159. Land Forms dependent on Climate. — In regions 
of ordinary climate the snow of winter melts in the spring, 
and the droughts of summer are not severe enough to make 
the surface barren by preventing plant growth. The form 
of such regions is determined largely by the action of 
streams and rivers, whose work goes on steadily along 
branches and trunk so that, in the course of ages, the 
land surface is dissected and a mature system of branch- 
ing valleys is carved. Many examples of regions of this 
kind have been giv-en in the descriptions of plains and 
plateaus, momitains and volcanoes. 

An excellent illustration of a well-dissected upland is 
found in the Ozark plateau of southern Missouri. The 
once even plateau has been transformed into a succession 
of rounded hills and spurs of graceful form, separated by a 
multitude of branching valleys. The maturely dissected sur- 
face has much less strength of relief than the plateau of 
West Virginia ; its slopes are usually of moderate steepness ; 
it is a fertile agricultural district. Villages are generally 
on the uplands, for most of the valleys are as yet too narrow 
to attract settlement. Many other examples might be named 
in which well-established branching valley systems testify 
to the long duration of an ordinary or normal climate. 

278 



DESERTS AND GLACIERS 279 

In certain other parts of the world the clhnate is so dry 
that vegetation is scanty or wanting, and the surface is left 
barren and desolate. Here streams flow only at rare inter- 
vals, the rivers frequently fail to reach the ocean, and the 
wind becomes an important means of moving land waste. 

In still other parts of the world the mean annual tem- 
perature is so low that the snowfall is not all melted away 




Fig. 143. The Ozark Plateau, Missouri 

in the warm season. The snow thus gathers from year to 
year, and, as it thickens, the under part is slowly com- 
pacted into ice. The ice has become thick enough to 
behave like a viscous body and to creep slowly down the 
slope of the land until it enters a warmer climate, where 
it melts away. Such moving sheets or streams of ice are 
called glaciers. Regions thus covered with ice and snow 
are even more barren than arid deserts. The removal of 
rock waste is there chiefly performed by ice instead of by 
rain and rivers. 



280 ELEMENTARY PHYSICAL GEOGRAPHY 

160. Deserts. — It has been explained in the paragraphs 
on rainfall that the arid deserts of the world occur under 
the drying trade winds, on the slopes and lowlands to the 
leeward of high mountain ranges, or in inclosed continental 
interiors. (See page 71.) The interior basins of Nevada 
and Utah, inclosed from moist winds by the ranges of the 
Pacific slope, fall under the third class, although they are 
less arid than many parts of the Sahara. 

All of these deserts are hot in summer, but they may be 
cool or cold in winter. They should therefore be thought 
of as prevailingly dry regions which may be hot or cold 
according to the season of the year. The deserts of cen- 
tral Asia have a mean January temperature of only 10° 
or 20° F. 

Rain seldom falls, and the dry air parches the dusty, 
sandy, or stony ground, so that plant life in deserts is 
scanty, though it is rarely altogether absent. Rock waste 
is plentifully exposed on open spaces between the scat- 
tered desert plants, instead of being covered by a close 
growth of grass, bushes, or trees, as in regions of more 
favorable climate. 

Deserts are of all forms, — mountains, j)lateaus, and 
plains ; but desert plains are the most extensive. The 
desolate gray forms of desert mountains, like the ranges 
of northwest Mexico (Sonora) and of northern Chile 
(Atacama), are much less picturesque than mountains 
with snowy summits and forested flanks in a moister 
climate ; but the wet-weather torrents of desert moun- 
tains have furrowed them with deep ravines like those of 
forested mountains. 



desp:rts axd glaciers 281 

161. Streams of Dry Climates. — When a light rain 
occurs in a region of dry climate much of the water 
returns to the atmosphere by evaporation, a large part of 
the remamder sinks into the thirsty soil, and the run-off by 
streams is small. Much of the ground water evaporates 
underground and passes out from the soil as vapor, instead 
of coming out in springs. When a heavy rain occurs, as 
occasionally happens, water is supplied faster than it can 
soak into the ground, surface rills form everywhere, and 
the streams are quickly flooded; but the floods soon run 
away, leaving the channels empty and dry again. 

The streams of dry regions are, therefore, very variable 
in volume ; active for a while after a rain, almost or quite 
disappearing in the long dry seasons ; advancing far down 
their lower courses when in flood, then dwindling and 
withering away and leaving their lower channels dry. 

In the Sahara dry water courses, known as wadies, are 
commonly used for roads, as their gorges frequently offer 
graded ways through rocky uplands. Death by drown- 
ing would nowhere be so little expected as in a desert; 
but it sometimes happens that a caravan, following a wady 
through an upland, meets a down-rushing flood, and before 
the travelers can climb the steep walls of the gorge they 
may be overwhelmed and drowned. 

In parts of the Rocky mountain region, of generally 
dry climate, heavy rains occasionally fall in summer. 
Then for a few hours the dry channels are flooded with 
a rushing turbid stream, which sweeps away the waste that 
has been washed in by lighter rains. Camping parties, 
pitching their tents too near a channel that is almost 



282 



ELEMENTARY PHYSICAL GEOGRAPHY 



dry in the afternoon, may be overwhelmed by a rushing 
flood at night. Opposite the mouths of canyons, streams 
of coarse waste, including bowlders weighing many tons, 
are spread forward by floods from cloud-bursts in the moun- 
tains,; — "immense, sudden, deluging rainstorms, which at 
rare and exceptional moments discharge their waters into 




Fig. 145. Flood in Cherry Creek, Denver, Colorado 



one of these mountain gorges. On such occasions bowlders 
six or eight feet in diameter are swept down the canyon 
in a fearful rush, and are sometimes carried out on the 
. . . slope for half a mile." 

Figure 145 illustrates a sudden flood in Cherry creek, 
where it passes through the city of Denver, Colorado. 
The channel of the creek was dry half an hour before 
this raging torrent appeared. 



DESERTS AND GLACIERS 283 

Streams that are supplied by springs in arid uplands 
and mountains frequently diminish in volume, partly by 
evaporation, partly by sinking into the ground, as they 
advance over desert lowlands. They may wither away 
and disappear entirely from the surface ; but their flow 
is usually continued as ground water for some distance 
beyond their visible end. Their load of waste is spread 
on the surface before them in the form of an alluvial fan. 
Many such streams are known around the mountains of 
Utah and Nevada. The depressions between the ranges 
are floored with fans and plains of waste that has been 
washed from the mountain ravines in time of flood. 

162. Bad Lands. — Arid regions of weak, fine-textured 
strata are often minutely carved by the wet-weather rills 
and rivulets bordering their chief valleys. This would not 
happen in a moister climate, for there the abundant plant 
growth would protect the surface and prevent the active 
run-off of the wet-weather rills ; but in an arid region, 
where plants are few or wanting, every little wet-weather 
rill erodes its own little ravine in the barren surface. 

Western Nebraska offers many examples of uplands that 
have been elaborately dissected in this way. Plate XII 
exhibits the delicately carved sides of a young valley in an 
even upland. Sharply carved forms of this kind are known 
as lad lands because of the difficulty of crossing them. 

163. Interior Basins and Salt Lakes. — The larger rivers 
of interior regions do not entirely wither away in their chan- 
nels, but continue until they reach a depression or basin be- 
tween the uplands. There the waters spread out, forming a 



284 ELEMENTARY PHYSICAL GEOGRAPHY 

lake. Evaporation from -the lake surface discharges as much 
water into the air as is received from the inflowing streams. 

In regions of more abundant rainfall the streams from 
a moderate drainage area suffice to fill lake basins to over- 
flowing. The Great lakes of the St. Lawrence system 
gather their water from a comparatively small area around 
each basin, yet they are always full, up to the outlet notch 
in their rim. In desert regions rainfall is so scanty and 
evaporation is so active that the streams from a large 
drainage area may form only a shallow lake, occupying 
a small fraction of its drainage area. 

Lakes of the latter kind are usually salt, for all the saline 
substances gathered in small quantity by their rivers accu- 
mulate in the lake and may in time constitute a fifth or 
even a third, by weight, of the lake contents. 

Great Salt lake of Utah, with about eighteen per cent 
of salt, is of this kind. It lies on the lowest part of the 
waste plain that has been built up in the depression among 
several mountain ranges. Its waters are so dense that a 
man's body will not sink beneath the surface. The Dead 
sea, with twenty-four per cent of salt, is one of the most 
famous salt lakes, occupying a long narrow depression in 
Palestine. Lake Van, in eastern Turkey, containing thirty- 
three per cent of salt, is the densest water body known. 

Interior basins, from which no rivers escape to the sea, 
receive the waste that the slopes of the inclosing moun- 
tains lose. The floors of the basins are in this way built 
up and smoothed. By the wearing down of the moun- 
tains and the filling of the basins the relief of the region 
as a whole is decreased. (See Figure 144.) 



DESERTS AND GLACIERS 285 

The level of the Dead sea is almost 1300 feet below 
that of the Mediterranean, and the bottom of the trough 
occupied by this sea is about 1300 feet deeper still. 
Ravines in the border of the uplifted plateaus lead 
down to stony fans that are advancing into the sea. 
The great depth of the water and the moderate exten- 
sion of the fans show that the basin contains much less 
waste now than it will in the future. 

A great part of Persia consists of large basins inclosed 
by mountains and wdthout outlet to the sea. Long waste 
slopes stretch forward five or ten miles wdth a descent 
of 1000 or 2000 feet, stony near the mountain flanks, 
and gradually becoming finer textured and more neai'ly 
level farther away. The central depressions are deserts 
of drifting sands, with occasional salt lakes. The popu- 
lation gathers around the margins of the basins where the 
dwindling streams are still running, avoiding the rugged 
and barren mountains on the one hand, and the unin- 
habitable central plains on the other. 

Central Asia repeats the same conditions on a still 
larger scale. The basin of Eastern Turkestan includes 
in its central part many low ranges that have been half 
buried with Avaste from the higher inclosing mountains. 
Many rivers flowing from the mountain rim wither on 
their way toward the chief central depression ; only the 
largest river (Tarim) reaches it, there spreading out in 
the marshy Lake Lob. The chief settlements are near 
the border of the basin, where the larger rivers come out 
from the mountains and where their waters can be used 
for irrisration. 



286 ELEMENTARY PHYSICAL GEOGRAPHY 

164. Wind Action in Deserts. — Where the land surface 
is covered with vegetation, the wind has little effect on 
the form of the ground. In arid regions where vegetation 
is scanty or wanting the wind becomes a powerful agent 
of change. The difference of wind action on a dusty road 
and on a grassy field may be taken to illustrate the con- 
trast between wind action in regions of dry and of wet 
climate. 

Wind storms in deserts raise the finest dust high into 
the air, drift along the sand at the bottom of the current, 
and rasp the unmoved stones and ledges with the drifted 
sand. 

Even in calm weather whirlv/inds are of daily occur- 
rence in deserts during the hot season. They are formed 
by the whirling ascent of air that has been heated by the 
action of sunshine on the dry bare ground. Before the 
whirl begins the existence of the overheated layer of sur- 
face air is often indicated by a mirage. 

Whirlwinds may raise dust more than a thousand feet 
into the air and drift it long distances before it settles. 
When violent winds blow, like the squalls which often 
precede thunderstorms in a moister climate, heavy clouds 
of sand and dust are raised from the desert surface, dark- 
ening the sky, and almost suffocating the traveler over- 
taken by them. 

Vessels in the Atlantic west of the Sahara sometimes 
have their sails reddened with dust brought by the trade 
wind from the Sahara. Rain in southern Europe is occa- 
sionally reddened with dust brought by storm winds from 
the same source. It has been estimated that, during four 



DESERTS AND GLACIERS 287 

days of such winds in March, 1901, nearly 2,000,000 tons 
of dust from the Sahara fell on central Europe ; the greater 
part reached the ground south of the Alps, but some of the 
dust was observed as far north as the Baltic sea. East of 
the deserts of central Asia extensive deposits of wind-borne 
dust have been formed; they constitute some of the most 
fertile districts in the Chinese empire. 

Desert mountains and uplands are so well exposed to 
strong winds that the finer particles of rock waste are 




Fig. 146. Sand Dunes in the Sahara 

blown from them, leaving their surface rocky and ston)\ 
The finer particles settle chiefly in the depressions where 
the winds are less violent; here the surface is sandy 
or dusty. 

165. Sand Dunes. — When the rocks of a desert are of 
a kind, like granite, that affords sand on weathering, the 
wind may blow the sand grains into drifts or dunes. 
Dunes sometimes grow to a height of from 500 to 600 
feet. Their surface may be delicately rippled, as in 
Plate XIII. In a region of relatively steady winds the 
sand is blown up the windward slope and carried over 
the crest; hence the dune may slowly advance, gradually 



288 ELEMENTARY PHYSICAL GEOGRAPHY 

changing its place and form. Dunes of drifting sand are 
usually more barren than other parts of a desert. 

A group of dunes sometimes advances across a dry val- 
ley, concealing its form for several miles. When rain falls 
the stream from the upper part of the valley disappears as 
it enters the loose sand of the dunes. 

Sand dunes occur also on low coasts where the winds 
frequently blow landward across a sandy beach. The 
dunes then form a belt of hills a little inland from the 
beach, as will be again referred to under shore forms. 

166. Dry Regions, formerly Moist. — • In some regions 
now arid, marks of a former moist climate are found. 
Certain basins now almost without water have been filled 
with great lakes, even to overflowing; the former shore 
lines of the lakes are marked by clift's, beaches, and deltas, 
and an outlet is sometimes traceable in a trench across the 
lowest pass in the inclosing highlands. 

The basin of Great Salt lake in northwestern Utah in 
prehistoric times contained a much larger lake, to which 
the name of an explorer, Bonneville, has been given. Its 
shore lines are still plainly recorded on the mountain sides 
nearly 1000 feet above the desert plain ai-ound the present 
lake ; the foreground of Figure 86 shows an extensive beach 
of this lake. The channel of an outlet leads northward 
across a pass to the basin of Snake river ; hence the former 
lake must have been fresh. The change from the moister 
climate of Lake Bonneville time to the drier climate of 
to-day has caused the almost complete disappearance of the 
lake waters, revealing the sediments of the lake floor in 



DESERTS AND GLACIERS 



289 



an arid plain. The ancient lake deltas are now trenched 
by the streams that built tliem. 

Another extensive lake (Lahontan) of very irregular 
outline and several smaller lakes once occupied the now 
desert basins of western Nevada. 




m -^ 



Fig. 147. Lakes Bonneville and Lahontan 



Compare the area of Lake Bonneville and that of Great Salt lake 
(fine and coarse dots, Figure 147). How long is Lake Bonneville 
from north to south? How long is Great Salt lake from northwest 
to southeast? (Scale of figure, 200 miles to an inch.) 

The causes of climatic changes of this kind are little 
understood, but their geograpliical consequences are of 
great importance. Extensive lakes among forest-clad 
slopes have been replaced by desert plains between arid 
mountains. 



290 ELEMENTARY PHYSICAL GEOGRAPHY 

167. Salinas. — Certain basins that formerly contained 
salt lakes have now been more or less completely dried 
out, leaving marshy or dry plains of salt, known as salinas, 
in the central depressions, avoided by all plant and animal 
hfe. 

The Bolivian table-land, a lofty waste-filled basin lying 
between two great ranges of the Andes, holds Lake Titi- 
caca in its northern part at an altitude of 12,500 feet. 
The outflowing stream runs 100 miles southeast to a 
marshy sahna, fifty miles long. The water not evaporated 
here flows southwest and is lost in a broad salina of daz- 
zling white surface. Somewhat farther south is a more 
extensive salina, 4000 square miles in area, a white and 
level plain covered with a layer of salt about four feet 
thick, impassable when wet, but firm in the dry season. 

Salt lakes and salinas yield common salt and other min- 
erals of commercial value. Great Salt lake is estimated 
to contain 400,000,000 tons of salt. These products 
would be of greater utility if they did not so generally 
occur in thinly populated desert regions. 

168. Ice Sheets and Ice Streams. — In the polar regions 
the temperature even in the lower atmosphere is so low that 
snow and ice cover much of the land all the year round, 
even close to sea level, cloaking the ground with ice 
sheets. In the temperate and torrid zones it is only on 
mountains that the temperature is low enough for snow 
to be more abundant than rain, so that snow fields are 
formed on the higher slopes and ice streams in the upper 
valleys. 



DESERTS AND GLACIERS 291 

During winter in the northern United States there are 
frequent examples of the formation of small short-lived 
ice sheets, after a succession of snowstorms with prevalent 
cold weather and occasional thaws. Such an ice sheet is 
not thick enough to move ; but if it should grow year after 
year to a thickness of 1000 or more feet, it would slowly 
move outward from the region of greatest height and 
thickness to lower ground in a milder climate. This is 
because ice is not perfectly solid ; it moves toward its 
unsupported border very much as a thick mass of paste 
would move, but much more slowly. 

169. Antarctic Ice Cap. — A few explorers of the far 
southern ocean have discovered a great ice sheet ending 
in cliffs that rise from 100 to 180 feet above the sea. No 
land was seen back from the top of the cliffs. 

Although as yet known only on one side of the south 
pole, the ice sheet is thought to form a polar ice cap, per- 
haps 1000 miles in diameter. There may be some land on 
which the cap rests ; but it is believed that much of it lies 
on the sea bottom. It must tend to thicken from snow 
supply over its desert plateaulike center ; but it slowly 
creeps toward the free seaward margin, where great tables 
of ice break off and float away as icebergs. As far as this 
desolate region has been explored it is uninhabited. 

170. The Greenland Ice Sheet. — Greenland is covered 
by a heavy sheet of ice, measuring about 1500 miles north 
and south and from 300 to 600 east and west. It has a 
slightly convex surface and probably rises to a height 
of 9000 feet in the central part. The ice sheet 3onceals 



292 ELEMENTARY PHYSICAL GEOGRAPHY 

the hills and mountains except near the margin, where 
the sheet is thinner ; here occasional rocky summits rise 
above the surface like islands in a frozen sea. 

Some of the Greenland glaciers (arms of the ice sheet 
descending toward or into the sea) are from ten to fifty 
miles broad. Their forward movement is from twenty 
to fifty feet a day. Many icebergs are formed of great 
fragments broken from their front. The interior of the 
ice sheet is a monotonous desert of snow and ice, now 
melting and becoming almost impassable, now freezing 
over or receiving a new layer of snow. 

The only inhabitants of this great cold desert are a 
minute worm and a simple microscopic plant that some- 
times gives a red color to snow. The Eskimos of Green- 
land live on the narrow belt of land between the ice sheet 
and the shore. j 

171. Alpine Glaciers. — Glaciers of the Alpine type flow ' 
slowly down in streamlike tongues from snow basins in the 
valley heads between lofty peaks and ridges. j 

The end of a glacier, melting as the ice descends to a ' 
milder climate than that of its gathering ground, often 
reaches below the tree line. Glaciers of this kind occur in 
the Alps, the Caucasus and Himalaya mountains of the 
Old World, and in the mountains of Canada, Alaska, 
and Patagonia in the New World. In Alaska many of 
the glaciers descend to the sea. The front of the Muir 
glacier, Plate XIV, breaks off in cliffs 200 feet high. 

A glacier moves faster along the middle surface line 
than at its sides or bottom, thus resembling a river. The 



DESERTS AND GLACIERS 



293 



movement of Alpine glaciers is on the average from 100 
to 600 feet a year. 

Glaciers press heavily on their beds, dragging rock 
waste beneath them and scouring the bed-rock clean and 
smooth. Loose grains and fragments of rock, dragged along 
by the ice, scratch and groove the smoothed rock surface. 
The rock waste 
thus scoured from 
the ice floor, as 
well as that torn 
from projecting 
ledges and that 
received - in rock 
slides and ava- 
lanches from sur- 
mounting slopes, 
is dragged or car- 
ried along by the 
ice and laid down 
around its lower 
margin or at its 
end, or washed 
away by the stream that issues from beneath the ice. 
Great bowlders may be carried on the ice. 

The ridge of rock waste that is ordinarily formed around 
the end of a glacier is called a terminal moraine ; one is 
shown in Figure 148. Note the moraine that trails down 
on the Rosegg glacier from a rocky spur between two of 
its upper snow basins. It is called a medial moraine. 
Why does it not follow the middle of the glacier? 




Fig. 148. Rosegg Glacier in the Alps 



294 



ELEMENTARY PHYSICAL GEOGRAPHY 



Describe the medial moraine of the Viesch (pron. feesK) gla- 
cier, Figure 149. From^ how many snow basins is this glacier 
supplied ? 

Large glaciers are sometimes so heavily covered with 
moraines near their lower end that a plant-bearing soil is 

formed upon them. Pas- 
turage is found for the 
flocks of the mountaineers 
in the Himalayas on cer- 
tain grass-covered mo- 
raines overlying the ice. 
Some Alaskan glaciers 
bear large forests on the 
moraines near their ends. 
Water received from 
side streams and supplied 
from melting ice gathers 
beneath a glacier and 
issues from an ice cave 
at its end. The water is 
usually whitened by fine 




Fig. 149. Viesch Glacier in tlie Alps 



"rock flour" 
beneath the ice. 



^round 



172. The Work of Ancient Glaciers and Ice Sheets. — Cer- 
tain parts of the world show the marks of ancient glacial 
action, although the climate there to-day does not allow 
snow to remain on the ground through the summer. 

Ancient glaciers occupied certain valleys in the Rocky 
mountains of Colorado and in the Sierra Nevada of Califor- 
nia. Great glaciers descending from the high Sierra into the 



DESERTS AND GLACIERS 



295 



desert lowland in eastern California built strong moraines 
forward from the mountain base at the mouth of the valley. 

Compare the glacier that once occupied the valley in Figure loO 
with the Rosegg glacier, Figure 148. 

Around the border of the Alps the lower land near the out- 
let of the chief valleys is often inclosed for ten or twenty 
miles from the mountains by a belt of hilly morainic ridges. 
The ancient glaciers that descended southeast from Mt, 
Blanc to the river- 
made plain of the 
Po built a huge 
terminal moraine, 
whose ridges rise 
from 1000 to 1500 
feet above the 
plain and inclose 
a great amphi- 
theater. 

The most ex- 
tensive ice sheets 
of the glacial 
period were those 
that spread outward from the highlands of Canada across 
the basins of the Great lakes upon the northern part of the 
United States, and from the highlands of Scandinavia across 
the Baltic upon northern Germany. (See Figure 144.) 

The highlands of eastern Canada, — the Laurentian high- 
lands, — whence the ice sheets moved out to the surround- 
ing regions, show much bare rock, clean scoured or covered 




Fig. 150. Glacial Moraines, Sierra Nevada, California 



296 



ELEMENTARY PHYSICAL GEOGRAPHY 



by a thin, stony, infertile soil. The hollows between the 
rounded rocky hills were often deepened by the ice, so that 
they now hold lakes or swamps, large and small. Besides 
many such lakes in rock basins, others are held behind 
barriers of rock waste or drift that was left irregularly 
over the surface when the ice melted away. 




Fig. 151. Glaciated Area of the Northern United States 

/' Much of the rock waste that has been swept from 
Canada by ice action is now found spread out in smooth 
plains, forming the fertile prairies south of the Great 
lakes. Rock waste that has thus been dragged along by 
ice action or washed along under or in front of the ice by 
streams is known by the general name of glacial drift. 

The Scandinavian highlands and the lowlands of north- 
ern Germany exhibit the same relation to ancient glaciation 
that has just been described for the Laurentian highlands 
of Canada and the states bordering the Great lakes. The 
highlands are left with scanty soil and much bare rock; 



DEtSERTS AND GLACIERS 



297 



the lowlands are sheeted over with drift, much of which 
is fertile farming country. The highlands remain in great 
part a wilderness, although scattered farms and small 
villages are found in the valleys. The lowland plain has 
a large agricultural population and many busy cities. X 

Among the most characteristic results of ancient glacial 
action are the rounded shapes of scoured ledges, Figure 
152, and the irregular surface of the moraines, Figure 153. 




Fig. 152. Ice-Worn Rocks, Coast of Maine 

Terminal moraines of stones, gravel, and sand are 
strongly developed in the states south of the Great 
lakes. They form belts of hills commonly from three 
to ten miles wide ; the hills are from fifty to two hundred 
feet high. The moraines are sometimes very uneven, 
with so many stony mounds and marshy hollows as to 
present a formidable barrier to travel. One may easily 
lose his way on such an undulating surface, where the 
hills are all much alike and where no conspicuous land- 
marks serve as guides. 



298 



ELEMENTARY PHYSICAL GEOGRAPHY 



Morainic hills are frequently dotted over with large 
rocks or bowlders, large and small, brought from some 




Fig. 153. Glacial Moraines, North Dakota 

more or less distant ledges by the ice; the bowlders are 
frequently unlike the rock on which the moraine lies. 




Fig. 154. A Glacial Bowlder 



Glacial bowlders are so plentiful in some parts of New 
England as to make the land there almost worthless. 



DESERTS AND GLACIERS 



299 



173. Drumlins. — In some districts the rock waste has 
been gathered beneath the ice sheet in arched, oval hills 
called drumlins, commonly half a mile or more long and 
from 100 to 200 feet high, easily recognized when once 
known. They may be compared to sand bars in rivers or 
to sand dunes under the wind. 




Fig. 155. A Drumlin, Massachusetts 



174. Valleys, Lakes, and Waterfalls in Regions of Ancient 
Glaciers. — Some of the ancient glaciers of mountain regions 
were very massive, from 2000 to 5000 feet thick, and moved 
with relative rapidity down channels of rapid descent ; here 
glacial erosion was most intense. The channels thus occu- 
pied are now seen as broad troughlike valleys with steep 
walls, deepened from 500 to 1000 feet or more beneath 
the side valleys that once joined them at even grade. The 
streams from the side valleys plunge down the rocky walls 
of the deepened main valley, forming fine waterfalls. Dis- 
cordant side valleys of this kind are called hanging valleys. 

Many hanging valleys are found in the Alps and in the 
mountains of Norway and Alaska; in the latter regions 



300 



ELEMENTARY PHYSICAL GEOGRAPHY 



the deepened main valley is usually occupied b}- an arm of 
the sea, called a fiord. (See page 320.) 
^ The rivers of a region that has been overridden by an 
ice sheet are often greatly disordered. At one place a 








Fig. 156. A Side Valley hanging over the Valley of the Ticiuo, 
Southern Alps 

valley floor may be scoured out, producing a rock basin. 
Lakes occupying such basins have been mentioned as com- 
mon in the rocky highlands of eastern Canada. At another 
place the irregular distribution of rock waste or drift may 



DESKRTS AXL> GLACIERS 



301 



turn a stream to a new course, where it is now seen cut- 
ting a steep-walled gorge with many rapids and falls. A 
lake is often formed upstream from the drift barrier. x 

The Adirondacks resemble the Black mountains of North 
Carolina in being dissected, subdued mountains, but the 
northern group possesses numerous lakes and gorges 




Fig. 157. Lake iu the Adirondacks, New York 

(" chasms ") wliich are wanting in the southern group. These 
peculiarities result from glacial action, which the Adiron- 
dacks suffered in common Avith the other northern parts of 
the country, but which the southern mountains escaped. 

When a river is displaced by barriers of glacial drift 
it must carve a new channel. Before the time of the ice 
action the river may have had a well-graded course ; now 
its flow is interrupted by falls and rocky rapids. Hence 
the displaced streams of glaciated regions supply much 
water power for mills and factories. 



302 ELEMENTARY PHYSICAL GEOGRAPHY 

Many rapids and falls of this kind occur in the streams 
of the northern United States and Canada. It must be con- 
cluded that the streams have not yet had time to establish 
graded courses since the ice melted away, and therefore 
that the ice sheet covered the country not long ago, as 
streams measure time, even though it was thousands of 
years ago, as time is counted by man. 

The Merrimac is a famous river of this kind. Its falls 
at Manchester, Lowell, and Lawrence have determined the 
growth of great manufacturing cities. Rochester, Grand 
Rapids, Minneapolis, and many other important cities 
have grown up at the side of falls on rivers that have 
been turned from their former channels by glacial drift. 

QUESTIONS 

Sec. 159. What is meant by an ordinary climate ? How are land 
forms carved in regions of ordinary climate ? What are the condi- 
tions of a land surface in an arid climate ? in a cold climate ? 

160. How are arid deserts related to the wind system ? Consider 
their climate as to heat, cold, and dryness. Describe their surface 
as to vegetation and rock waste. What are the forms of deserts? 

161. How is rainfall disposed of in a dry climate ? Describe the 
streams of dry regions. What is a wady? What danger attends 
the use of a wady as a roadway ? Describe the floods of the di-ier 
parts of the Rocky mountain region. Describe a flood at Denver. 
How may streams end in desert lowlands? What becomes of their 
load of waste ? Where is their flow continued ? 

162. 163. Under what conditions are bad lands formed? 
Describe their form. Where do they occur ? What becomes of the 
larger rivers of interior basins? What is the i-elation of inflow and 
evaporation in lakes without outlets ? in lakes with outlets ? Com- 
pare the lake area with the drainage area in the two cases. Why 



DESERTS AND GLACIERS 303 

are lakes without outlets usually salt ? Describe Great Salt lake ; 
the Dead sea. How is the form of interior basins changed ? Describe 
the basin of the Dead sea ; the basins of Persia ; of central Asia. 

164, 165. Compare wind action on plant-covered and on barren 
surfaces. Describe the action of whirlwinds in arid regions ; of 
violent winds. How far is dust carried by the wind? "Where do 
deposits of wind-borne dust occur ? Describe sand dunes as to origin, 
height, form, movement. Describe the dunes of coasts. 

166, 167. Describe the ancient shore lines of the Great Salt lake 
basin. AVhat do they prove ? Describe another similar example in 
Nevada. How do the two differ? What is the present condition 
of these two basins? What are salinas? Describe an example. 

168, 169, 170. Where do ice sheets occur? When may a short- 
lived ice sheet be seen ? Describe the movement of an ice sheet. 
What is known and what is supposed about the Antarctic ice cap? 
Describe the Greenland ice sheet. How are glaciers and icebergs 
related to this ice sheet ? Where do the Eskimos of Greenland live ? 

171. Describe a glacier of the Alpine type. Where do such 
glaciers occur ? How does a glacier move ? AMiat work does it 
perform? Describe a terminal moraine ; a medial moraine. State 
the relation of vegetation to certain moraines. 

172, 173. How has the occurrence of ancient glaciers been discov- 
ered? Where have such glaciers existed? AVhat remains have they 
left? Where did the most extensive ancient ice sheets occur? What 
effect was produced by the North American ice sheet in eastern Can- 
ada? in the northeastern United States? What is glacial drift? 
Describe the effects of the ancient ice sheet of northwestern Europe. 
Describe the terminal moraines south of the Great lakes. What are 
glacial bowlders ? Where are they plentiful ? What are drumlins ? 

174. What are hanging valleys? Explain them. Where do they 
occur? What effect have ancient ice sheets had on drainage? 
Describe the drainage of the Laurentian highlands. Compare the 
Adirondacks and the Black mountains. • What effect have displaced 
streams on industries ? Name some examples. 



CHAPTER X 
SHORE LINES 

175. The Border of the Lands — Next to the prospect 
gained from a lofty mountain, the view of the sea from 
the border of a highland is the most inspiring sight 
that the earth offers. To the traveler from an inland 
country it is as if the shore line marked the beginning 
of a new kind of world. There is the mystery of the 
distant horizon, far beyond which strange lands are hid- 
den. There is the unceasing movement of the waves as 
they roll upon the beach, and of the tides as they slowly 
rise and fall; and the thought comes that thus the ocean 
has been rolling in waves, rising and falling in tides, 
ever since the lands and the waters were divided. With 
the sight of the vast ocean comes the thought of unend- 
ing time. 

While the surface of the land has been for ages 
attacked by rain and rivers, the border of the land lias 
been attacked by the sea. The sun warms the air in 
the torrid zone, and thus the general circulation of the 
atmosphere is established. The winds beat on the ocean 
and form waves, and the waves run ashore and dash in 
surf upon the lands. The border of the land is worn 
back under so constant an attack, and the waste taken 
from it by the surf, as well as that washed into the sea 

304 



SHORE LINES 



305 



by livers, is slowly carried away into deeper water by the 
waves, the currents, and the tides. In time the area of 
the land would be greatly reduced by the invasion of the 
sea, were it not for upheavals of the earth's crust by 
which the land is now and then, here and there, renewed. 





/ ?;._ 












i 




1 






RH 


^B^^ISk'^w' ' 




H 


H 




mm 


B 


^^^^^ 


m 


^^^ 





Fig. 158. Sea Cliffs, Grand Manan, New Brunswick 

176. The Work of the Sea on the Shore. — Where the 
border or coast of the land dips under the sea the water 
lies against it and marks the shore line. The waves and 
other agents work upon the shore and produce changes 
in its form. Hence the outline of any shore line depends, 
in the first place, on the form that the land had when its 
present attitude with respect to the sea was taken, and 
in the second place on the changes afterward made by 
the shore processes. 



306 ELEMENTARY PHYSICAL GEOGRAPHY 

The agitation of sea water in waves is greatest at the 
sea surface and gradually decreases downward; but the 
large waves cause some slight disturbance even at depths 
of several hundred feet. The movement of water iu 
waves is not steadily forward in the direction in which 
the waves travel, but repeatedly 'to and fro over small 
distances. The larger the waves and the shallower the 
water, the greater effect their agitation has on the bottom. 
Fragments of rock, large and small, are thus moved back 
and forth according to their size and to the strength of 
the waves. The fragments wear each other as well as 
the rocky ledges on which they are rolled and thrown. 
Thus the edge of the land is worn back by the sea, the 
shallower parts of the sea are slowly deepened, and the 
waste is slowly removed to deeper water offshore. Little 
work of this kind is done in calm or fair weather; but 
during storms the processes of grinding and transporta- 
tion are actively at work, shaping the shore line and the 
shallow sea bottom. 

The currents of shore waters are chiefly of tidal origin, 
but they are also sometimes parts of the general circulation 
of the ocean. Except in narrow channels, they are seldom 
strong enough, unaided, to move the waste that is strewn 
over the bottom ; but when the waste is jostled by waves 
it slowly shifts along in the direction of the current. 

If deep water reaches close to the land, the waves spend 
most of their strength close to the shore line, breaking vio- 
lently on the headlands, whence they sweep loose material 
out to the deeper bottom ; there it rests in comparative quiet. 
Bare rock is abundantly exposed on shores of this kind. 



SHORE LINES 307 

If the land descends slowly under the sea, the shore is 
fronted by shoal water ; then much of the strength of the 
waves is spent on the shelving bottom before they reach 
the shore line. Rock waste is so slowly removed from a 
shore line of this kind that beaches of gravel and sand 
are commonly strewn along it ; the waters offshore become 
somewhat turbid during storms with fine waste raised by 
strong waves from the shallow bottom. 

177. Different Kinds of Shore Lines. — Two kinds of 
shore lines have already been described. In one the sea 
lies upon a smooth coastal plain that was once a sea bot- 
tom (page 144) ; in the other it lies on the flanks of a 
depressed mountain range (page 211). These two kinds 
are the types for many other examples. 

Shore lines of the first kind are smooth and simple, and 
are bordered by shallow water. Shore lines of the second 
kind are irregular and are generally bordered by deep 
water. Those of the first kind border lowlands of weak 
strata ; they have few good harbors and hence they do not 
offer good opportunity for traffic between land and sea. 
Those of the second kind generally have rocky headlands 
and islands inclosing protected bays, where harbors are 
numerous and trading settlements are favored. 

178. Shore Lines of the First Kind. — The low plain of 
Buenos Aires dips gently beneath the sea, whose waters 
are shallow for many miles off the simple shore line. 
Large vessels cannot approach close to the land, except 
where an artificial harbor has been dredged out, 



308 ELEMENTARY PHYSICAL GEOGRAPHY 

When storm winds blow from the sea they sweep the 
water upon the low coast and cause destructive sea floods ; 
dikes are built along certain parts of the shore to keep 
the waters off. 

The waves along the shallow shores of lowlands beat 
up the bottom sands and in time build offshore sand reefs 
inclosing narrow lagoons. The movement of currents along 
the sand reef forms a beach, straight or gently curved on 
its seaward side. On-shore winds blow sand from the 
beach and build sand hills or dunes of irregular form, 
sometimes fifty or one hundred feet high, on the reef. 
Flood and ebb tidal currents maintain passages, called 
inlets, through the reef, as at X>, Figure 159. 

Sediments are brought into the lagoons by streams from 
the land, and, with the aid of salt-water plants, the shallow 
lagoons are gradually filled and converted into salt marshes 
at high-tide level. Sand reefs, lagoons, and marshes are 
plentiful along the Atlantic and Gulf coast of the United 
States. 

A sand reef is slowly worn back by the action of the 
surf on its beach. The dune sands are slowly blown back 
into tlie narrowing lagoon or upon the lagoon marsh. At 
last the lagoon and its marsh disappear, and the mainland 
is directly attacked and cut back in a low bluff. The 
retreat of the sand reefs may be more rapid on one stretch 
of the shore than on another ; thus one part, CA, Fig- 
ure 159, may have a bluff cut in the mainland, while 
'another part, AB, is still fronted by reef and lagoon. 

The coast of New Jersey is fronted by long sand reefs 
inclosing lagoons and tide marshes. Farther north at 



SHORE LINES 



309 



Long Branch, a noted seaside resort, the land is abeady 
cut back in a low bluff. Severe storms cut away the base 
of the bluff, sometimes undermining the houses that are 
built too close to it. 

The low coast of the middle Netherlands has retreated 
two miles or more in historic times. A belt of dunes, 
half a mile or more wide, lies inland from the smooth 




Fig. 159. Diagram of a Lowland Coast with Bluff and Saud Reef 

Draw an outline map illustrating the features of Figure 159. 
Draw another map representing an earlier stage in the development 
of this shore, line, when the whole length of shore was fronted by a 
reef and before any bluff had been cut. Draw a third outline show- 
ing a later stage, when the retreat is great enough to produce a bluff 
nearly all along the shore line, leaving only a small part fronted 
with sand reef and marsh-filled lagoon. 

harborless beach. The chief ports are on the lower 
courses of rivers, whose channels are broadened by the 
flow and ebb of the tides. 

The Romans built a castle back of the dunes, near the 
mouth of the Rhine. In 1520 the dunes had blown 
inland, grain by grain, and the sea had cut the shore back 
close to the castle. In 1G94 the castle stood in the sea. 



310 ELEMENTARY PHYSICAL GEOGRAPHY 

about half a mile from land. In 1752 it disappeared, 
destroyed by the waves. 

In 1460 a church that had been built inside the dunes 
in the Dutch village of Scheveningen (near The Hague) 
was reached by the sea. A new church was then built 
about a mile inland, at the east end of the village. In 
1574, the outer part of the village having been gradu- 
ally consumed by the waves, new houses had been built 
east of the church, so that it stood in the middle of the 
village. In a later century the new church again stood 
close to the shore, the village having moved beyond it. 

In southwestern France the west winds, sweepmg in 
from the Bay of Biscay, have formed a belt of dunes two 
or three miles wide. Formerly the sand was drifted far- 
ther and farther inland with every westerly gale. Fields 
and villages were invaded and buried by the advancing 
drifts. Now most of the dunes have been planted with a 
kind of pine tree that thrives in a sandy soil ; the wind is 
lifted from the sand by the trees, and the sand drifts have 
ceased advancing. The pine forests yield much resin. 

179. Sea Cliffs. — As the margin of a plain is cut back 
by the sea, the shore bluff increases in length and height, 
until it may deserve the name of cliff. The cliff face 
weathers ; fragments, large and small, fall from it to the 
beach below, where they are moved about and ground to 
pieces by the waves. The fine particles are drifted off- 
shore to deeper water. Thus longer and longer stretches 
of the shore become harborless, and traffic between land 
and sea is greatly hampered. 



SHORE LTXES 



311 



In northwestern France the upland plain of Normandy- 
fronts the sea in a vertical sea cliff, 200 or 300 feet high, 
with gently curving shore line for many miles. A large 
part of the plain must have been consumed by the sea in 
the development of the cliff. 




Cliffs of Xormandy (looking southwest) 



180. Shore Lines of the Second Kind. — These shore 
lines are more varied than those thus far described. When 
an uneven land surface is depressed and partly covered by 
the sea, numerous ridges and hills stand forth as promon- 
tories and continental islands, valleys are entered by arms 
of the sea, and protected harbors are plentiful. The irreg- 
ular coast of Maine offers many illustrations of this kind. 
Its relief is of moderate measure. 

The waves beat furiously on the exposed headlands of 
irregular coasts during storms. Angular rock fragments, 



312 



ELEMENTARY PHYSICAL GEOGRAPHY 




Fig. 161. Diagram of an Irregular Shore Line 



weathered from the rocky coast, are swept about by the 

dashing waves and are in time rounded to cobbles and 

pebbles, and 
worn down to 
sand. These 
fragments bat- 
ter the shore 
and erode the 
margin of the 
land, gradually 
forming a cliff 
that rises above 

sea level and a bench that is partly bare at low tide. 

Isolated rock columns or stacks stand for a time on the 

rock bench. At high tide the waves roll across the bench 

and sometimes 

excavate sea 

caves, fifty or 

more feet in 

length, at the 

base of the cliff. 

Fingal's cave, 

on the island 

of Staffa, west 

of Scotland, 

and many other 

less famous caves have thus been eroded by the waves. 
As the wave-cut bench broadens and the cliffs increase 

in height, some of the rock waste is swept alongshore 

from the headlands into the little coves and bays, forming 




Fig. 1()2. Diagram of an Irregular Shore Line with 
Cliffed Headlands and Beached Bays 



SHORE LINES 



313 



beaches on the more protected parts of the coast line. 
Such beaches present a smooth curve, concave to the 
sea ; here the surf breaks in even rollers, quite unlike the 
dashing and fretting waves on the ragged headlands. 

Dj-aw maj)s of selected parts of the coast shown, in Figures 161 
and 162, on a somewhat larger scale than that of the figures, and 
thus illustrate the change from the original to the later outline. 

The cobbles and pebbles thrown up on the beaches dur- 
ing storms may form a wall five or ten feet above high 
tide. A pond or 
swamp is often %^ ~^^^^^.W^^^ .^" :-- ; <^^M^M/k!L 



inclosed behind 
tlie wall beach 
in the valley 
that had previ- 
ously opened 
into the bay. 
The New Eng- 
land coast has 
numerous beaches of this kind between its rocky headlands. 

Compare the coast forms in Figures 161, 162, and 163. Where 
has the sea gained on the land ? the land on the sea ? 

The promontory of Brittany in western France, beaten 
by heavy waves and swept by strong tides, is in about the 
stage of development represented by Figure 162. The 
headlands are dangerous on accomit of the rocky reefs 
that rise to half-tide height on the rock bench that fronts 
the ragged cliffs. The small bays are partly filled with 
curved beaches of cobbles, pebbles, and sand. 




Fig. 163. Diaa:raiii of a Curved Shore Line 



314 ELEMENTARY PHYSICAL GEOGRAPHY 

As time passes, headlands are cut farther back, so that 
the cliffs become higher and longer. The bays are more 
and more filled with beaches and cobbles, gravel and sand, 
and with deltas formed by streams entering the bay heads. 
Thus the outline of the shore becomes more regularly 
curved than it was at first, and convex lines of cliffs 
alternate with concave stretches of beach. 

Fine examples of shores in this stage are found in 
parts of southwestern England. The cliffed headlands 




Fig. 164. A Cliffed Heacllaud and a Land-Tied Island 

are guarded by lighthouses ; settlements are usually found 
in the river mouths of the beached bays. The coast of 
western Italy and the northern coast of California offer 
many examples of this kind. 

181. Land-Tied and Sea-Cut Islands. — Irregular coasts, 
formed by the depression of a mountainous region, are 
often originally fronted by islands. Such islands not infre- 
quently come to be attached to the mainland by the back- 
ward growth of sand reefs that are supplied with waste 
from the outer cliffs. Compare the two headlands of 



SHORE LINES 



315 



Figure 1 64 in this respect. A land 
of Italy is shown in Plate XYI. 

The fortified Rock of Gibraltar, 
belonging to Great Britain, was 
originally an island, but is now 
tied to the mainland of Spain by 
a broad sand reef. Part of the 
reef is "neutral ground," occu- 
pied by neither Spain nor Great 
Britain. 

If the coast is of unequal 
strength along its front, the rate 
of sea cutting may vary from 
place to place, and thus parts of 
the coast may in time be cut off 
from the mainland and form 
islands, as in Figure 166. Many 
islands in the bay of Panama are 
thus formed. They are remnants 



tied island on the coast 




Europa Poinf 



Fig. 165. Gibraltar 




Fig. IGO. Diagram of a Group of Sea-Cut Islands 



316 



ELEMENTARY PHYSICAL GEOGRAPHY 



of the mainland whose extent has been much reduced by 
the attack of the sea. The width of the isthmus of 
Panama has thus been lessened and the length of the pro- 
posed interoceanic canal across it has been correspondingly- 
shortened. 




Fig. 167. A Cliffed Coast iu Alaska 



182. Cliffed Coasts. — Coasts that have been long 
exposed to strong waves and tides may have been cut so 
far back that no part of the original outline remains. In 
such cases a nearly continuous cliff, sometimes of great 
height, fronts the shore, as in Figure 167. Traffic between 



SHORE LINES 



317 



land and sea is practically impossible on such a coast. A 
vessel wrecked on the ragged bench beneath the cliffs can 
receive little succor while stormy weather lasts. 

The Orkney and Shetland islands, north of Scotland, 
have lost much of their former area by the attack of the 
sea. The head- 
lands are cut off 
by lofty cliffs, 
some of which are 
nearly 1000 feet 
high. An isolated 
stack, known as 
the "Old Man of 
Hoy," rises 600 
feet above the sea. 

183. Elevated 
Shore Lines. — 

When the devel- 
opment of shore 
lines is interrupt- 
ed by a change in 
the level of the 
land, the work of 
cliff cutting and bay filling must be begun again at a 
new level, in much the same way as before. 

If the land rises, the former shore line may be found 
at a greater or less distance inland from the new shore 
line. This has already been referred to in the descrip- 
tion of coastal plains. 




Fig. 168. The " Old Man of Hoy " 



318 ELEMENTARY PHYSICAL GEOGRAPHY 

An elevated shore line, marked chiefly by rocky cliffs and 
benches with occasional beaches, may be traced along a 
great part of the western coast of Scotland at a height of 
from twenty to twenty-five feet above the sea level of to-day. 
The narrow coastal plain that slopes forward from the old 
shore line to the new one is pictured in Figure 64. This 
elevated shore line forms a convenient bench along v/hich 
roads may be laid near the base of the slopes that ascend 
to the highland summits. Old sea caves, roughly walled 
in, sometimes serve as stables for the seaside farmers. 

A low bluff, seeming to be a former shore line, has 
been traced on the coastal plain of Virginia and North 
Carolina, a short distance inland from the present shore 
line. Lines of ancient sea cliffs at several different 
levels break the coastal slopes of Cuba and form steps 
in the broad plains of eastern Patagonia. 

The western coast of Norway is bordered for much of its 
length by a belt of lowland and islands, sometimes as 
much as from three to ten miles wide, from whose inner 
margin an old sea cliff rises to the highlands (Figure 169). 
The lowland is a broad rock bench or platform, cut by the 
sea when the land stood about 300 feet lower than now. 
A large part of the population of western Norway dwells 
on this ancient sea floor. 

The former sea cliff, at the inner margin of the jDlat- 
form, is from 500 to 1000 feet high. A number of 
rocky hills stand on the platform, representing uncon- 
sumed islands of the former shore. 

The withdrawal of lake waters by a change of climate 
(page 288) has an effect on the condition of shore lines 



SHORE LINES 



319 



similar to that produced by an elevation of the land with 
respect to the sea. The cliffs and beaches that contour 
around the slopes of the mountains of Utah, where the 
waves of Lake Bonneville once beat, in many ways 
resemble the elevated shore lines of western Scotland, 

Well-defined ancient shore lines, consisting of cliffs and 
beaches, are found in the region of the Great lakes. The 




Fig. 169. The Coast Platform of Norway 

shore lines are found to converge toward depressions in the 
height of land to the south of the lakes, and well-defined 
channels are there discovered. This indicates the former 
existence of lakes much larger and deeper than those 
of to-day, Avith outlets southwestward to the MississipjDi 
system, instead of northeastward by the St. Lawrence. 

These facts are explained by supposing that the 
melting ice sheet of the glacial period obstructed the 
St. Lawrence valley, so that the lake waters had to rise 



320 ELEMENTARY PHYSICAL GEOGRAPHY 

high enough to overflow southwestward. Many of the 
beaches are so distinct that they are used as naturally 
graded roadways. The outlet of the expanded Lake 
Erie ran past the site of Fort Wayne, Indiana, to the 
Wabash river. The outlet of the expanded Lake 
Michigan led past the site of Chicago to the Illinois 
river; this channel is now followed by the artificial 
drainage canal by which some of the water of Lake 
Michigan is again led along the line of ancient outlet. 

184. Fiords. — The valleys in the highlands of Norway 
have been deepened by the heavy and strong-moving glaciers 
that once filled them. Since the glaciers disappeared the 
sea has entered the deep channels that the ice scoured out, 
forming long, narrow, and deep embayments, called fiords^ 
often deeper at the middle than near the mouth. Their 
depth has probably been increased by a depression of the 
region, by which the border of the ice-scoured lowland has 
been converted into a swarm of islands. 

The rock walls of the fiords are so steep that few set- 
tlements can be made along them, except at their heads 
or where deltas are built by side streams that cascade 
from the hanging valleys (see page 299) of the high- 
lands. Roads can seldom follow the shore lines ; hence 
communication is chiefly by water. 

An irregular coast of this kind has often favored the 
development of maritime arts. Its outlying islands tempt 
exploration ; its protected bays afford safe harborage even 
for small boats. The people occupying the coastal lands 
become expert sailors and fishermen. 



SHORE LINES 



321 



The numerous bays of southern Scandinavia were known 
as viks to the people who occupied them 1000 years ago, 
and the inhabitants were therefore called vikings, or bay 
people. They became bold marauders, invading the more 
southern coasts of western Europe, by whose people the 




Fig. 170. A Delta in a Norwesriau Fiord 



vikings were called Northmen. Normandy is to this day 
named after these early sea kings. They were the first 
European people to venture far out upon the ocean, and 
thus almost 1000 years ago they discovered Greenland 
and otlier parts of the western world. 

The west coast of Patagonia (southern Chile) resembles 
that of Norway in the possession of deep fiords among 
bold mountains. The Canoe Indians dwell here, — a 



322 ELEMENTARY PHYSICAL GEOGRAPHY 

primitive people who find the steep slopes of the land 
so inhospitable that they live almost entirely in open 
canoes on the water. A small fire is kept burning on a 
few sods in the canoes, so that it may be carried from 
place to place. These Indians have no fixed habita- 
tions and make little use of the land, except when 
they build temporary shelters of tree branches, roughly 
thatched, in one cove or another where they stop for a 
time to gather shellfish. 

The mountainous coast of Alaska is varied by numer- 
ous fiords, into some of which great glaciers descend from 
snowy ranges in the background. As in Norway, much 
of the coast is so steep as to be unfit for settlement. 
Hanging valleys frequently open on the walls of the fiords, 
500 or more feet above sea level. 

185. Delta Shore Lines. — Rivers tend to build their 
deltas forward, and thus oppose the destructive action of 
the sea. The Mississippi discharges a great quantity of 
land waste into the Gulf of Mexico. The waters of the 
gulf are relatively shallow, and the tides are weak. Here 
the outline of the delta seems to be governed entirely by 
the action of the great river (Figure 136). 

The several distributaries of the Mississippi build low 
and slender banks of mud on each side of their channels 
faster than the waves can wear them away ; hence the 
delta has several fingerlike projections into the sea. In 
order to increase the depth of water in one of the channels, 
or "passes," jetties (dikes of wood and stone) have been 
built forward beyond the end of the delta fingers, thus 



SHORE LINES 



323 



increasing the current and forcing it to~scour the channel 
to a depth sufficient for seagoing vessels to enter on their 
Avay to New Orleans. 

The Rio Grande, a large river, but much smaller than 
the Mississippi, delivers land waste to the gulf in greater 
quantity than the waves 
and currents can altogether 
remove ; hence its delta is 
built forward (Figure 171). 
But the waves are strong 
enough to smooth the out- 
line of the delta; hence it 
has a gently convex curve 
without fingerlike projec- 
tions. The Brazos and Col- 
orado rivers, about midway 
between the Mississippi and 
the Rio Grande, also cause 
a slight forward bowing 

of the Texas coast. Fig. 171. Deltas of the Texas Coast 




186. Effect of Climate on Shore Lines. — Shore lines, 
like land forms, are affected by climate ; not only by 
differences between regions of onshore and offshore winds, 
where waves and currents are stronger or weaker, but even 
more by differences of temperature. 

Iif^olar seas the land is often bordered by a fringe of 
ice called the ice foot. During the winter the ice foot 
usually remains attached to the land, unless broken by 
strong tides ; in summer it may loosen and float away. 



324 



ELEMENTARY PHYSICAL GEOGRAPHY 



It is often used as a longshore roadway for sled travel by 

Eskimos and Arctic explorers. 

In warm seas the shores that are not exposed to strong 

surf may be invaded by certain kinds of trees, forming a 

network so dense as to make landing difficult. 

The mangrove is the most important tree of this kind. 

It grows freely in 
shallow sea water 
on low and muddy 
shores, and protects 
the land from the 
waves. Muddy sedi- 
ments accumulate 
in the quiet water 
among the trees, and 
thus the land gains 
on the sea. Shores 
all overgrown with 

Fig. 172. Mangrove Tree mangrove SWamps 

are dismal as com- 
pared with the clean shell-strewn beaches of sand and 
pebbles beaten by trade-wind surf. 




187. Coral Reefs. ^ The shallow waters of continental 
borders or mid-ocean islands in the warmer seas are 
commonly occupied by coral reefs, composed of the 
limy framework of coral animals. Living corals are 
found chiefly on the outer side of the reef, where they 
grow in the shallow water much in the same way that a 
thicket of small bushes grows' on the land. They take 



SHORE LINES 



325 



the limestone needed for their skeletons from solution in 
the sea water. 

When reef-building corals first take possession of the 
shallow waters on a shoal or near a shore line, their growth 
extends upward from 
the shallow bottom and 




Fig. 173. A Fringing Reef 



outward into the surf. 
Blocks and branches are 
detached from the bot- 
tom by severe storms 
and rolled about by the waves ; the larger fragments are 
thrown together, forming a beach a little above sea level ; 
the finer particles are carried toward deep water and strewn 
over the sloping bottom. The reef thus broadens, and if 
near the land, it forms a fringe close along the shore line. 
At this stage it is called a fringing reef. 

Strips of fringing reef are found on the equatorial coast 
of eastern Africa, along parts of the Brazilian coast, at 
various points on the coast of Cuba and elsewhere in the 

West Indies, and border- 
ing many islands in the 
Pacific, as the Hawaiian 
and other groups. The 
Galapagos islands in the 
eastern Pacific, close to 
the equator, are free from reefs, because of the low tem- 
perature of the water brought there by the strong Peruvian 
current. (See Figure 112.) 

Draw maps of the islands and reefs shown in Figures 173 and 
174. Compare the two. 




Fig. 174. A Barrier Reef 



326 



ELEMENTARY PHYSICAL GEOGRAPHY 







Fig. 175. Part of the Great Barrier Reef of Aiistralia (as seen at low tide, 
looking toward tlie mainland) 

188. Barrier Reefs. — A fringing reef broadens by the 
outward growth of the corals, and the submarine slope is 
built forward by the supply of coral fragments. At the 
same time water supplied by rain, by streams from the land, 



SilOKK LINES 



327 




Fig. 176. Diagram of Part of a 
Barrier Reef 



and especially by the surf that rolls over the reef, slowly dLs- 
solves and washes away the inner part of the reef where liv- 
ing corals are few or wanting. Thus the reef may come to be 
separated from the land 
by a shallow lagoon a 
mile or more wide ; and 
in this way a fringing 
reef may change to a 
barrier reef. 

The Great Barrier reef 
stretches along the north- 
east coast of Australia 
for about 1000 miles, 

the largest reef in the world. It is usually from twenty 
to fifty miles from the mainland, mostly beneath sea level, 
interrupted by numerous inlets, and bearing a few low 

islets. The sea outside 
descends rapidly to great 
depths ; the water inside 
is shallow (from ten to 
forty fathoms). 

189. Effects of Eleva- 
T, .„„ ^. r^.-^, , tion. — If a slow uplift 

Fig. 177. Diagram of Part of an Elevated '■ 

Reef with a New Fringing Reef OCCUrS, COrals will con- 

tinue to grow on the 
outer face of the reef, but the body of the reef may be 
raised above sea level, forming a terracelike bench above 
the new shore line, outside of which new fringing reefs 
grow. Compare Figures lit) and 177. 




328 



ELEMENTARY PHYSICAL GEOGRAPHY 



An uplifted reef, forming a bench at a height of about 
thirty feet, with a breadtli of a mile or less, borders much 
of the northern coast of Cuba. The sea has worn a low 
cliff in the front of the bench ; from the cliff top one may 
look down upon the new fringing reef now growing in 
the sea. 

The loose texture of uplifted reefs allows them to be 
worn down again with relative rapidity. While the 
uplifted reef is thus wasting away, the fringing reef may 
be growing outward vigorously and changing to a barrier 
reef. The uplifted reef will be in part dissolved by the 
solvent action of rain water ; and it may, after elevation 
ceases, be reduced below sea level. A shallow body of 
water, or lagoon, will thus be formed within the new 
barrier reef. 

190. Atolls. — If the central island within a barrier or 

fringing reef is worn away or is lost by slow submergence 

as the reef grows upward 
and outward, the reef may 
make an irregular ring 
around an oval lagoon 
and the ring may slowly 
increase in size by the 
outward growth of the 

reef, while the lagoon is deepened by the dissolving action 

of its waters. 

Such a ring island is called an atoll. Many islands of 

this kind are known in the Pacific ocean. 




Fig. 178. Diagram of an Atoll 



Compare the reefs shown in Figures 173, 174, and 178. 



SHORE LINES 329 

Although one of the most wonderful objects in nature, 
a lonely atoll affords little opportunity for human devel- 
opment. The natives of such islands lead easy and indo- 
lent lives, but their progress toward better conditions than 
those of savagery is hindered by the small variety in their 
surroundings and by their distance from lands of more 
varied form and products. 




Fig. 179. An Atoll, or Coral Island 

The small height of atolls subjects them to the danger 
of being overwhelmed by earthquake waves. Hurricanes 
sometimes come upon them, unobstructed from the open 
sea, sweeping violent surf far up the beaches ; the storm 
winds break down the cocoanut palms on which the 
natives depend largely for food and for the materials for 
many of their simple arts. Atolls have no streams, but 
fresh water supplied by rains may be found not far below 
the surface. The thin soil has little variety of mineral 



380 ELEMENTARY PHYSICAL GEOGRAPHY 

matter, but floating pumice (frothy lava) is often cast 
ashore from distant volcanic eruptions, and some of the 
islanders have learned to gather and pulverize it to use 
as a fertilizer for their little fields. Floating logs from 
other lands sometimes drift upon the atolls, and their 
roots occasionally carry stones of firmer texture than 
coral rock (for example, fragments of dense lava from 
a volcanic island) ; rude whetstones, pestles, and mortars 
are made from these chance supplies. 

Although birds are plentiful, there were no mammals 
on coral islands until rats and mice came ashore from 
vessels; a few domestic quadrupeds have occasionally 
been imported by foreign residents. 

QUESTIONS 

Sec. 175. What is the origin of the forces by which the ocean 
works on the lands? How is the work done? What becomes 
of the material worn away? Why are the lands not completely 
worn away? 

176, 177. Upon what two conditions does the outline of any shore 
line depend ? Describe the movement of waves and their action on the 
lands. How are shore cm-rents caused? How do waves aid the work 
of currents? Compare the work of the sea in deep and in shallow 
shore waters. Describe the shore line of a young coastal plain ; of 
a depressed mountain range. Contrast them as to harbors, settle- 
ment, and trade. 

178. Describe the shore of the coastal plain of Buenos Aires. 
What effects are here caused by storm winds? by waves? What 
are the origin and torm of sand reefs? What are inlets? lagoons? 
salt marshes ? How are the sand reefs and lagoons changed by the 
action of surf ? Describe the coast of New Jersey ; of the Nether- 
lands ; of southwestern France. 



SHORE LINES 331 

179. What is the origin of sea cliffs ? How are they worn back ? 
Describe the cliffed coast of northwestern France. 

180. "What are the features of a shore line of the second class? 
How and on what parts of these shores do waves form cliffs? 
stacks? caves? beaches? What are wall beaches and where are 
they common? Describe the coast of Brittany. Describe the shore 
forms of later development. Where are they found? 

181. 182. What are land-tied islands? Describe an example. 
AVhat are sea-cut islands? Describe some examples. Describe a 
cliffed coast. AYhat is the relation of such a coast to human occu- 
pation ? Describe an example. AVhat is the " Old Man of Hoy " ? 

183. AA'hat changes in the shore line result from a change in the 
level of the land? Describe the elevated shore line of western Scot- 
land; of North Carolina. Where are other examples found ? Describe 
the western coast of Norway. Under what conditions were certain 
abandoned shore lines formed in Utah ? around the Great lakes ? 

184. What are fiords? Explain their origin. Where do they 
occur? How do they affect settlements? How does an irregular 
shore line affect the maritime ai'ts ? Give an example from Scandi- 
navia. Describe the Canoe Indians. What is the relation of hang- 
ing valleys to fiords ? 

185. How do rivers tend to opjiose the action of the sea? 
Describe the delta of the Mississippi ; of the Rio Grande. 

186. How does climate affect shore lines? What is the ice foot? 
Describe a mangrove swamp. Where is such a swamp formed ? 

187. 188. What are coral reefs ? Where are they found ? (See 
Figure 112.) How are they formed? What is a fringing reef? 
Where are fringing reefs found ? Why are no reefs found on the 
Galapagos islands? What is a barrier reef? How is it formed? 
Describe the Great Barrier reef of Australia. 

189, 190. Describe an uplifted reef. What changes may such a 
reef undergo^ What is an atoll? In what ways may atolls be 
formed? What opportunity do atolls afford for human develop- 
ment? To what danger are atolls exposed? 



CHAPTER XI 
THE DISTRIBUTION OF PLANTS, ANIMALS, AND MAN 

191. Geographical Aid in Human Progress. — The study 
of physical geography, or physiography, gives a knowl- 
edge of the features of the earth, so that we may better 
understand the relation of man and nature. This rela- 
tion is of great importance, because the progress of man- 
kind from the savage toward the civilized state has been 
largely made by taking advantage of favorable geograph- 
ical conditions and by learning to make greater and better 
use of the products and forces of the earth. 

The winds blew over the lands and waters, carrying 
rain and causing waves and currents, for thousands of 
years while man was an ignorant savage. When he 
invented sailboats and windmills a new use was made 
of the winds, and man profited greatly by his inventions. 
Streams had been wearing down the falls and rapids in 
their valleys and spreading rock waste over their flood 
plains during all the long existence of the continents. 
When man cultivated food-bearing plants on the flood 
plains and built flour mills by the waterfalls, he gained 
much from making new and good use of these natural 
forms and forces. 

The magnetic forces of the earth have always been capa- 
ble of directing a compass needle, but they were not used 

332 



THE DISTRIBUTION OF ORGANIC FORMS 333 

until man discovered liow a balanced magnetized needle 
would behave. Coal and iron ore lay untouched in the 
earth's crust for millions of years ; now the nations that 
make the fullest use of these invaluable resources have 
become the leaders of the world. 

Reference has frequently been made on the earlier pages 
of this book to the effects of geographical surroundings 
on the growth and distribution of plants and animals and 
on man's way of living. The present chapter reviews 
these effects and gives new examples of them. 

192. Life on the Earth. — The earth is known to have 
been occupied for ages past by various kinds of plants 
and animals, for their fossil remains are found in many 
rock layers of ancient origin. During all these ages 
living forms have tended to spread over as large a 
region as possible, just as they do now. 

Barriers of different kinds limit the spreading of 
organic forms. Land plants and animals are stopped by 
the sea, unless they can travel by water or air. Sea 
animals are stopped by the lands. Those forms that 
need a warm climate do not spread into regions of cold 
climate. Grazing animals that need abundant grass are 
stopped by deserts and by forested mountains. 

Plants growing from heavy seeds, like nuts, spread 
slowly from the parent plant. Plants growing from 
light seeds, especially from such as are carried by tlie 
wind, like the seeds of the dandelion, the thistle, and 
the fireweed, are very rapidly distributed. The dande- 
lion is found on the northern lands all around the earth. 



334 ELEMENTARY PHYSICAL GEOGRAPHY 

Certain kinds of sea animals, like mussels, barnacles, 
and corals, spend most of their life attached or rooted 
to the sea bottom, living on food that is brought "to 
them by the moving waves and currents. This reminds 
one of the dependence of rooted land plants on the mov- 
ing air for most of their sustenance. But the young 
forms of these fixed animals are free to float about, and 
are then carried far and wide by the currents of the sea, 
just as light seeds are carried by the winds. 

Most animals can move from place to place. They have 
fins for swimming, legs for walking, or wings for flying. As 
they wander about in search of food, they come in time to 
be distributed over all parts of the earth accessible and 
favorable to them. This is as true for the ancient history 
of life on the earth as it is for the life of to-day. 

Birds of strong flight are widely distributed. Walking 
birds and quadrupeds are more narrowly limited. The 
ostrich of Africa, the emu of Australia, and the rhea of 
South America are each confined to one of the southern 
continents. The albatross, a large sea bird, whose skill 
in flying without flapping its wings is very remarkable, 
is found all around the great southern oceans. 

Occasional examples of some fifty kinds of North 
American birds are found in western Europe ; but no 
stragglers from Europe are found in North America. 
This is because the prevailing westerly winds blow from 
North America toward Europe. The course of the winds 
is determined by the direction of the earth's rotation, and 
thus the rotation of the earth has an influence on animal 
distribution. 



THE DISTKIBUTIOX OF ORGANIC FORMS 335 

193. Geographical Factors in the Struggle for Existence. 

— The number of plants and animals in a given region is 
usually about as great as can be supported there. Where 
food is plenty the number of individuals is large ; this is 
usually the case in the shallow borders of the seas and 
on the lands of the temperate and torrid zones. The 
luxuriant plant growth of the forests under the equa- 
torial rains illustrates this rule. Where food is scarce, 
as in very dry and in very cold regions, the number of 
individuals is small; and some of the cold, snow-covered 
deserts are almost uninhabited, as in central Greenland. 

Man frequently causes great changes in the numbers 
of plants and animals, as when he cuts down the trees 
of a forest and plants grain in the new-cleared fields, 
or when he kills the wild animals of a region .and intro- 
duces domestic animals in their place. But apart from 
changes of this kind, the plants and animals of a region 
remain at about the same number for centuries. 

It is, however, well known that every kind of plant 
and animal tends to increase in numbers, for the seeds 
of plants and the offspring of animals are always more 
numerous than the individuals that produce them. A 
single grain of corn may grow to a stalk bearing several 
ears, each of which may bear over a hundred grains. 
Many thousand eggs are contained in the roe of a single 
salmon. If all the young plants and animals reached 
maturity and produced other young forms in their turn, 
the number of individuals would increase enormously. 

The reason that the number of plants and animals 
in a district does not greatly increase is that, in spite of 



336 ELEMENTARY PHYSICAL GEOGKAPHY 

the production of numerous young individuals, many of 
them perish in the severe competition for an opportunity 
to live. Many seeds fail to germinate because they fall 
on unfit soil, or because they are eaten by animals. 
Many young animals are devoured by other animals. 
As a rule, those individuals survive which have some 
advantage over their fellows and are therefore more fit 
to succeed in the "struggle for existence." The success 
of these individuals is often called the "survival of the 
fittest"; and the survivors are said to be chosen from 
those which perish by "natural selection." 

The chances of survival in the struggle for existence 
are increased for those plants and animals which are best 
adapted to their geographical surroundings. Fish have 
gained a shape that enables them to move easily through 
the water ; this is an advantage in getting their food and 
in escaping from pursuit. Many of tlie smaller animals 
of the open ocean move slowly ; but they imitate the 
transparence of sea water and so make themselves almost 
invisible and more likely to escape their enemies. 

As the earth is lighted from the sky, many animals 
whose backs are dark have lighter colors underneath, 
so as to counteract the effect of shade; they are thus 
less easily seen and so have a better chance of approach 
to their prey or of escape from their enemies. Animals 
inhabiting deserts are usually gray or tawny, imitating 
the color of the bare ground. In the snow-covered 
Arctic regions many animals are Avhite. 

Some animals gain protection by living in caverns or 
in the crevices of talus slopes ; others burrow in fine 



THE DISTRIBUTION OF ORGANIC FORMS 337 

rock waste or soil. Name some animals of these kinds. 
Some animals choose steep cliffs and high peaks for their 
home, so that they shall not be easily pursued. Eagles 
build theii' nests on inaccessible pinnacles, such as those 
of the spurs that separate the huge side ravines of the 
canyon of the Colorado in Arizona. What can you tell 
about the home of the Rocky mountain sheep (the bighorn) 
and of the chamois of the Alps ? 

194. Variation of Plants and Animals. — All the many 
existing kinds of plant and animal life are the descendants 
of a smaller number of more ancient kinds. But when 
the ancient forms, preserved as fossils, are compared with 
living forms, it is found that they are not alike. Through 
the millions and millions of years during which the earth 
has been inhabited there have been slow variations in the 
kinds of plants and animals living on it, so that those now 
living differ from their remote ancestors. The forms of 
life to-day are, as a rule, very unlike those whose fossils 
are found in the oldest fossil-bearing rocks. 

Among the many causes which have combined to pro- 
duce variations in plants and animals, none have been 
more important than changes in their geographical sur- 
roundings. While part of a sea bottom is slowly raised 
to form a coastal plain, the kinds of animals that once 
occupied this part of the sea floor must seek some other 
home ; at the same time the plants and animals of the 
neighboring older land have opportunity of taking pos- 
session of the young plain. As lofty mountains are 
slowly worn down to lowland peneplains, the forms of 



338 ELEMENTARY PHYSICAL GEOGRAPHY 

life that once occupied the higher mountains must adapt 
themselves to their new surroundings or perish. During 
the slow change of climate which caused the gradual 
advance and retreat of the great ice sheets that once 
covered eastern Canada and the northeastern United 
States, plants and animals were first driven away from 
these regions and later allowed to return to them. 

Changes of these kinds have repeatedly taken place 
in the earth's history, and it is probable that every one 
of them has caused some variation in the plants and 
animals of their regions. The plants and animals that 
we now find distributed over the world represent the 
present stage in the long series of varying forms. 

195. Life in the Seas and on the Lands. — The different 
parts of the earth are so unlike that it is natural to find 
striking differences among the plants and animals which 
have become fitted to occupy unlike regions. No geo- 
graphical contrast is greater than that between the sea 
floors covered by the oceans and the lands covered by the 
air. The kinds of plants and animals that have made their 
home on the lands have come to differ greatly from those 
that have for ages lived in the oceans. Hence continents 
and oceans must have existed for long ages because their 
plants and animals are now very unlike. 

A remarkable difference between land and sea life 
results from the much greater density of water than of 
air. Even the largest sea plants do not need strong 
trunks, but are supported by the water. Many sea ani- 
mals are no heavier than the water they live in ; hence 



i 



THE DISTRIBUTION OF ORGANIC FORMS 339 

they can float without exertion and all their strength can 
be given to swimming. The kinds of fish that sometimes 
rest on the water bottom lie upon it so lightly that they 
have no need of legs ; all their members are fins. Many 
kinds of fish and other marine forms spend their lives in the 
open ocean without approaching the shores or the bottom. 

Birds, on the other hand, are much heavier than the air 
through which they fly ; hence much of their strength must 
be used to prevent falling. Even the best flyers spend 
some of their time on the ground or on trees. When they 
alight the air gives them so little support that they need 
legs on which to walk about. 

It has been explained in earlier chapters that the deep 
ocean is monotonously cold, dark, and quiet, without 
changes of weather or seasons, and that the ocean bottom 
is usually a gently undulating plain covered with ooze or 
mud for thousands of miles together. The lands, on the 
other hand, are the seat of varied conditions. They pos- 
sess a great variety of form and material ; they experience 
changes from day to night, from summer to winter; they 
suffer many changes of weather from warm to cold, from 
calm to stormy, from clear to cloudy, from dry to wet. The 
development of the higher forms of life, such as are com- 
monly found on the lands, should be regarded as a conse- 
quence of the great variety of geographical conditions 
found there, in contrast to the monotony of the deep ocean, 
where the forms of life are of a much simpler order. 

Nearly all the flowering plants live on the lands. Water 
plants, especially those of the sea, are of a simpler kind. 
No plants live on the dark ocean floor, for plants cannot 



340 ELEMENTARY PHYSICAL GEOGRAPHY 

grow without sunlight. Many animals of the sea are 
attached, plantlike, to the bottom. Others move slowly, 
like starfish and shellfish; still others float with the drifting 
waters, having little movement of their own, like jellyfish. 
Only the more highly organized, like many of the fishes, 
move rapidly; but nearly all land animals move about 
actively, walking, running, or flying. 

The larger and more important laAd animals (mammals 
and birds) are warm-blooded. Most sea animals are cold- 
blooded, like the lower animals of the land. The only 
warm-blooded animals of the sea (whales, porpoises, seals, 
etc.) are believed to be the descendants of ancient land 
ancestors, gradually modified for the marine life which they 
have adopted. The reason for this belief is that the sea 
mammals still resemble in many ways the mammals of the 
lands. They bear their young alive and nourish them with 
milk from the breast ; they must come to the surface of 
the sea to breathe, for unlike fish they have no gills by 
which they can make use of the air that is dissolved in sea 
water. They differ from land mammals only in ways that 
make them better suited for life in the sea ; their legs have 
been modified into flippers for swimming ; and those forms 
which, like the whales, live altogether in the sea no longer 
have fur, like the land animals of a cold climate, but are 
protected from the cold of sea water by a layer of fat or 
" blubber " under their skin. 

Many land animals have developed organs for the pro- 
duction of sound, the most remarkable sounds being the 
song of birds and the speech of man. The animals of the 
sea are, with hardly an exception, silent. 



THE DISTRIBUTION OF ORGANIC FORMS 341 

The greater intelligence of many land animals than of sea 
animals should also be regarded as a result of the develop- 
ment of land animals amid a greater variety of geographical 
conditions than is found in the seas. The class of insects, 
almost limited to the lands, furnishes many examples of 
extraordinary instincts, such as those of bees and ants. 
Nest building by birds, house building by beavers, " hom- 
ing" of pigeons, and 



trailing (by scent) of dogs / 
are examples of highly v 
developed instincts 
among land animals that 
have no parallel among 
the animals of the sea. 

The wonderful intel- 
ligence of man has been 
developed on the lands, because only on the lands is to be 
found the great variety of form, climate, and products 
which can stimulate the development of high intelligence. 
It would have been as impossible for man to develop as an 
inhabitant of the dark and monotonous ocean tioor as it 
has been for civilization to arise on the frozen and lone- 
some lands of the Antarctic regions. 




Fig. 180. Beavers 



196. Life on the Continents. — The arrangement of the 
continents has exerted a great influence on the distribution 
of land plants and animals. It has been stated that the north- 
ern continents are nearly united around the Arctic circle, 
and that three great extensions of this northern land belt 
stretch southward; Africa being most closely associated 



342 



ELEMENTARY THYSICAL GEOGRAPHY 



with the northern lands of the Old World, South America 
being less closely associated with North America, while 
Australia is cut off from Asia by the sea. It is there- 
fore natural to find many resemblances among plants 
and animals in high northern latitudes, and to find that 
differences among them become greater and greater as 

middle and low latitudes are 
passed and far southern lati- 
tudes are entered. 

The lichens and mosses of the 
frozen northern lands are similar 
all around the Arctic circle. 
The animals of the same region 
include the polar bear, rein- 
deer (called caribou in North 
America), lynx, musk ox, and 
Arctic hare, which are of the 
same kind on all the lands 
around the north frigid zone. The northern lands must 
therefore have once been connected, and their connection 
must have occurred at so late a period in the history of the 
earth that there has not since then been time enough for 
these Arctic animals to become unlike in their now some- 
what disconnected homes. 

In the lower latitudes of the northern hemisphere the 
plants and animals of the lands possess certain resemblances 
that prove their descent from a common ancestry, but they 
also show certain marked differences that prove the separa- 
tion of the continents in these latitudes for a very long 
period of time. 



\ 




Fig. 181. Caribou 




THE DISTRIBUTION OF ORGANIC FORMS 343 

* 

The puma and jaguar of the New World are catlike 
animals that resemble in many ways the lion and leopard 
of the Old World. The resemblance is so strong that it 
must be believed they are descended from a common stock ; 
hence in some former time the Old and New Worlds must 
have been connected in latitudes where the ancestors of 
these animals could pass from 
one region to the other ; but this 
connection ceased so long ago 
that distinct differences have 
since then arisen between the 
two groups of catlike animals. 

The long separation of the 
Old and New Worlds is con- 

n. J 1 ri T J • 1 , Fig. 182. Jaguar 

farmed by fandmg certain plants 

and animals peculiar to each region. Horses, cattle, and 

other domestic animals, as well as tea, coffee, and wheat, 

originated in the Old World, while humming birds and 

rattlesnakes, as well as maize (corn), potatoes, and cactus 

plants, are peculiar to the New World. 

The differences among the animals of the three southern 
continents are strongly marked. The giraffe, hippopotamus, 
and many kinds of antelopes are found only in Africa ; but 
that continent shares with the adjacent lands of southern 
Asia the lion, elephant, rhinoceros, and the manlike apes. 

South America stands more alone : here are found mon- 
keys with prehensile tails, tapirs, llamas, sloths, and arma- 
dillos, none of which are found in the Old World. 

In Australia, the most isolated of the southern conti- 
nents, nearly all the quadrupeds belong to the peculiar 



344 



ELEMENTARY PHYSICAL GEOGRAPHY 



group of marsupials or pouched mammals, which carry the 
young ill a pouch on the breast of the mother. The best 
known marsupial is the kangaroo. Australia contains also 
the lowest kind of quadruped, the water mole (or duckbill), 
which resembles birds in laying eggs from which its young 
are hatched. 

It is not because Australia is unfitted for mammals that 

they are not native there. 
Rabbits have been carried 
from Europe to southern 
Australia, where they 
have become so numerous 
as to be a nuisance. Shecj) 
are now raised there in 
great numbers, so that 
Australia has become an 
important wool-growing 

Fig. 183. Kansraroo , rpii -i p 

* country, ihe absence oi 

mammals in Australia must therefore be explained by the 
long separation of that land from the continents on which 
mammals were developed. In the same way, the absence 
of Australian forms in other parts of the world is not due 
to differences of food supply or of climate, but to the long 
separation of the island-continent from the other lands. 
The eucalyptus, a large Australian tree, thrives in the mild 
climate of California and southern Europe. So horses and 
cattle, brought from Europe to the New World, have 
become numerous on the prairies and plains of North 
America, and on the llanos and pampas of South America. 
Potatoes, native to America, have become an important 




THE DISTRIBUTION OF ORGANIC FORMS 345 

food supply in Europe. What can you tell about the 
English sparrow? 

197. Races of Mankind. — It is not only in the distri- 
bution of the lower animals that the grouping of the con- 
tinents has had a controlling influence. The several races 
of mankind, differing in language, religion, and form of 
government as well as in color, originally occupied regions 
that correspond in a general way to the grand divisions of 
the lands. Hence it may be believed that the separation 
of the continents by the oceans, aided by certain mountain 
and desert barriers, has been the chief cause of the division 
of mankind into races. 

The greatest of the continents, Eurasia, contains two 
races. The European race, generally light colored but 
with some dark-skinned families, has its home in Europe, 
Africa north of the Sahara, and southwestern Asia. The 
leading nations of this race are the most advanced peoples 
of the world. They have developed liberal governments 
in which the rights of the people are considered, and have 
advanced greatly in the cultivation of the arts and sciences. 

The Asian race is found chiefly in eastern, central, and 
northern Asia; it is often called the Yellow race. China 
contains the greatest number of this race, the Chinese 
being separated from the Hindus of India (a branch of 
the European race) by the lofty mountains of the Hima- 
layan system. Although comparatively advanced in many 
arts, the Asians have acquired little knowledge of the 
sciences, and their governments are usually despotic. The 
Japanese are to-day their most advanced nation. 



346 ELEMENTARY PHYSICAL GEOGRAPHY 

America is the home of the American or Red race ; its 
native inhabitants are divided into many tribes, each led 
by a chief. Africa, south of the Sahara, is the home of the 
African or Black race, governed by despotic kings or 
chiefs. Australasia and the peninsulas and islands of 
southeastern Asia include certain black and brown races. 
Few nations among these races have made important 
advances toward civilization. 

Within the last few centuries the means of travel over 
land and sea have greatly increased, and to-day the races 
of mankind are by no means limited to the continents 
named above as their homes. People of European ancestry 
now make the chief part of the population in North and 
South America, southern Africa, Australia, and New 
Zealand, as well as in Europe. The Chinese are not 
limited to China alone, but are found as merchants and 
laborei'S in the islands of southeastern Asia, Australia, 
and elsewhere. Many descendants of the African race 
are now living in North and South America. 

It should be noticed that, while the people of the Euro- 
pean race are now widely distributed over all parts of the 
world, and while Asians and Africans are found in large 
numbers in other lands than their homes, few of the less 
advanced races have entered Europe, the chief of these 
being members of the Asian race, the Turks in the south- 
east and the Finns and Lapps in the north. 

198. Life on Islands. — Islands that rise from conti- 
nental shelves are occupied by many plants and animals 
similar to those of the neighboring mainland. It is inferred 



THE DISTRIBUTION OF ORGANIC FORMS 



347 



from this that the continental mass once stood higher than 
now and that the continental shelf was then a lowland on 
which the present islands rose as hills or mountains. The 
forms of life that were then widespread have become sepa- 
rated by the submergence of the lowlands and the division 
of the islands from the continent. 

Various species of cassowaries, large ostrichlike birds 
unable to fly or swim, are found in 
Australia and on the hilly islands 
to the north, each land area having 
its own species. From this it is 
supposed that the ancestral family 
of all these species occupied the 
region when the continental mass 
stood higher and the mainland and 
islands were connected by the low- 
land now under water in the con- 
tinental shelf. Since then it is 
believed that the region has been 
depressed and the lowland flooded 
by the sea, while the higher parts 

remain as islands separated from Australia and from each 
other. The differences between the various species of 
cassowaries must have arisen since their family was divided 
by the drowning of the lowlands. 

Many of the islands near Australia resemble that con- 
tinent in possessing marsupials. The islands nearer Asia 
have no marsupials, but possess many mammals similar to 
those of the mainland to which they are related. A belt 
of deep water divides the two groups of islands. 




Fig. 184 



348 ELEMENTARY PHYSICAL GEOGRAPHY 

Islands that rise from the deep ocean floor far from the 
continents have no large native animals, but are occupied 
by such forms of animals and plants as might have reached 
them through the air or the water from the nearest larger 
land. 

The Azores, a group of mid-ocean volcanic islands in 
the North Atlantic, are so called from the hawks that 
were common there when the islands were discovered by 
voyagers from Europe. The Galapagos islands of similar 
origin in the Pacific west of Peru are named from the 
large tortoises that abound on them. 

199. Climate as a Control of the Distribution of Plants 
and Animals. — Differences of temperature resulting from 
the globular form of the earth are of great importance in 
limiting the distribution of plants and animals. Plants 
like palm trees, that flourish in the torrid zone, spread into 
lands of higher latitudes on both sides of the equator until 
they reach regions where the summers are too cool for 
them to mature their fruit. Plants that occupy the tem- 
perate zones are limited to belts -on whose polar side the 
summer is too brief and cool and on whose equatorial side 
the summer is too hot for their seeds to ripen. Thus in 
the central United States cotton is limited to the southern 
states, corn flourishes best near the middle of the country 
from the Ohio to the lower Missouri, and wheat is pro- 
duced most abundantly in the northern states. In these 
northern latitudes there are great forests of pines and 
other cone-bearing trees. Still farther north, where the 
ground is frozen all the year round, except for a little 




Pr.ATi; XVIII. Forest in ilie Equatorial Kain Belt. Ceylon 



THE DISTRIBUTION OF ORGANIC FORMS 349 

melting during the short summer, trees are wanting and 
vegetation is reduced to stunted and herbaceous forms, 
with many mosses and lichens. (See Figure 112.) 

The various kinds of animals are, like plants, limited to 
regions in which the summers are long and warm enough 
— but not too warm — for them to rear their young. But 
unlike plants, which live on mineral food derived from the 
soil and the air, animals subsist either on. animal or vege- 
table food; and flesh-eating animals, like the lion, often 
devour plant-eating animals, like the antelope. Thus in 
the end all animals depend for food directly or indirectly 
on plants ; hence the distribution of animals depends in 
part on the distribution of plants, and this in turn depends 
on climate. 

Examples of the distribution of animals according to 
zones of temperature are found in the limitation of the 
caribou, moose, and elk to the northern parts of America; 
of the alligator, tapir, and sloth to low latitudes; and of 
the rhea to far southern America. 

200. Climate as a Control over the Customs of Savage 
Tribes. — The customs of mankind ai-e influenced in many 
ways by climate. Some of the climatic influences are 
direct, as with regard to clothing and shelter. Some influ- 
ences are indirect, as with regard to food supply, which in 
turn is affected by the distribution of plants and animals. 
Climatic influences are less apparent on civilized people 
than on savage tribes; for the former have developed 
world-wide commerce, and thus gather supplies from all 
parts of the earth; while the latter know little or nothing 



350 ELEMENTARY PHYSICAL GEOGRAPHY 

of regions away from their own home. Two examples are 
given in the following paragraphs. 

The equatorial belt of Africa is in large part a densely- 
forested wilderness, because of its plentiful rainfall. Tall 
trees spread their branches aloft, shading the ground all the 
year witli their heav}^ foliage. Vines and creepers climb the 
trees and hang from bough to bough in great festoons, and 
the shady and damp ground is covered with a thick growth 
of bushes with stems and branches so closely interlaced that 
it is almost impossible to make one's way through them 
without cutting a passage. Even the wild animals of the 
forest go and come by paths that they keep open by fre- 
quent passing. Objects near at liand are hidden from sight; 
the explorer cannot tell what is ahead of him in the gloom 
of the forest until he is close upon it. Vegetation is here 
so luxuriant that it is a burden upon the people who live 
amid its abundant growth. 

Some of the savages of this great forest are Dwarfs, from 
three to four and a half feet in height. They wear little 
clothing, for the air about them is always warm. They do 
not try to malce clearings and to cultivate fields, but search 
out the more open parts of the forest and build their 
villages where the undergrowth is least dense. They have 
some trade with other tribes, but live chiefly by hunting 
wild game, which is plentiful. Although entirely ignorant 
of many simple arts practiced by peo[)le of more open 
countries, the Dwarfs are expert in all the ways of forest 
life. They can travel (i[uickly through the woods, know- 
ing all the paths and open places. They protect their 
villages from the attack of neighboring tribes by planting 



THE DISTlillU'JMON OF ORCANIC FORMS 



351 



sharpened stakes in the paths of appicKUjh. 'I'liey dig pit- 
falls in the narrow forest paths, covering them with sticks 
and leaves, and in this way capture even the larger wild 
animals. They prepare a poison from certain plants and 




b'i<i. IHS. Dwarfs in tin; Kquatorial Forest 

tip their speai-s and arrows with it. In spite of their small 
size they are formidable enemies to invaders of their forest 
home. 

The desolate shores of rireenland present conditions of 
an entirely diffei'ent kind. Extreme cold prevails there 
during the long dark winter, and most of the land is 
covered all the year round with ice and snow, — a vast cold 



352 



ELEMENTARY PHYSICAL GEOGRAPHY 




desert. A narrow belt along the coast is free from snow 
in summer, and here live a few tribes of Eskimos; but 
the ground is so barren that they get little support from 
it. The only treelike plants are of stunted growth, sel- 
dom over two or three feet high. The herbage consists 
chiefly of mosses and lichens, which grow for a time in 
summer when the frozen ground is thawed for a few inches 

below the surface. A 



small supply of wood 
comes from the trunks of 
trees that are occasion- 
ally drifted by ocean cur- 
rents to the Arctic shores 
from warmer regions ; 
but there is so little of it 
that many articles which 
might be made of wood elsewhere are here made from the 
bones of sea animals. 

The Eskimos wear heavy fur clothing. They travel in 
sleds drawn by dogs over the snow-covered land or the 
frozen sea. They make slender canoes, called kayaks, 
which they paddle very skillfully when hunting seals and 
walruses. Until visited by Europeans and Americans, the 
Eskimos were as ignorant of the rest of the world as were 
the African Dwarfs; yet so well have they learned to take 
every advantage of their frigid surroundings that they sur- 
vive where men from a more civilized nation, unused to 
living in so barren a region, might perish. 

These brief accounts of the Dwarfs and the Eskimos show 
very clearly that, as a rule, the climate and the other local 



Fig. 186. Eskimo hunting Walrus 



THE DISTRIBUTION OF ORGANIC FORMS 353 

features of the regions in which they live exercise a strong 
control over their manner of living. The Eskimos know 
nothing of forests, thickets, and pitfalls. The Dwarfs 
know nothing of snow and ice, sleds, kayaks, and har- 
poons. But each of these groups of people has become well 
practiced in certain habits and customs that enable them 
to secure food, shelter, and reasonable safety of life; and 
these habits and customs are closely related to the surround- 
ings in which they have been acquired. The further the 
world is examined, the more general this rule is found to be. 

201. Effects of Change of Seasons on Plants and Animals. 

— In the torrid zone the chief seasonal contrasts of the 
year are between the dry (hot) and wet seasons. During 
the dry season vegetation withers, but with the coming 
of the -wet season all forms of plant life grow actively. 
This is particularly marked on the desert borders of the 
subequatoiial rain belt, where the ground may be bare and 
dusty in the dry season and covered with vegetation in 
the wet season, as on the llanos of Venezuela. 

In higher latitudes the chief seasonal contrasts are 
between the cold and warm seasons, or winter and sum- 
mer. In winter vegetable growth is almost or quite sus- 
pended, but with the approach of summer growth begins. 
Some trees, like the pines, bear the winter with little vis- 
ible change. Others, like the oaks, drop their leaves in the 
autumn, and hence this season is often called fall. Trees 
of this kind pass the winter with bare branches. Still other 
plants are killed by the coming of cold weather, and only 
their seeds survive the winter ; these are called annuals. 



354 ELEMENTARY PHYSICAL GEOGRAPHY 

Animals also have many devices for surviving the 
winter. Some are hardy enough to bear all sorts of 
weather, and may be seen searching for food through 
winter cold as well as summer heat ; wolves and foxes are 
of this kind. Others retreat into caverns and crevices 
and lie torpid during the cold months, coming forth lean 
and hungry in the spring ; bears and snakes have this 
habit. Many insects are like the annual plants in being 
killed by cold weather, leaving their eggs to be hatched 
on the return of higher temperatures in the spring. Many 
birds escape winter weather by migrating to a warmer region 
in the autumn and returning poleward in the spring. 

All these peculiar habits result from the oblique position 
of the earth's axis with respect to the plane of its orbit, by 
which the change of seasons is caused. 

Changes in habit of life with changes of season are 
not limited to plants and the lower animals. Man also 
responds in many ways to seasonal changes from heat to 
cold, from dryness to rainfall. In continental interiors 
of temperate latitudes, where most of the rainfall is in 
summer, the wandering of noma-dic tribes is largely con- 
trolled by search for pasture for their flocks ; as on the 
plains or steppes north of the Caspian sea. Again, in 
Algeria, on the northern border of the Sahara, summer 
pasture is found chiefly on the mountain slopes ; but when 
the winter rains begin (subtropical rains) the herdsmen 
drive their flocks down to the lower lands, that were dusty 
and barren deserts a few months before. 

Planting and harvesting are characteristic occupations 
of the warmer months among the more advanced peoples 



THE DTSTRIBUTIOX OF ORGAXIC FORMS 355 

in all temperate climates ; during the colder months agri- 
cultural labor is in less demand. In the north temperate 
zone there is the great advantage of an abundant land area 
with a winter that is cold enough to require the storage of 
food and a summer tliat is warm enough to provide the 
food to be stored. The leading nations of the world have 
arisen in this zone, and there can be little doubt that the 
habits of industry and thrift here made necessary, but 
not too difficult, by geographical conditions have been of 
great importance in bringing civilization out of savagery. 

202. Plant and Animal Life on Lofty Mountains. — 

Climate varies not only from equator to pole, but also from 
lowlands to mountains. On accomit of the lower tempera- 
ture and the heavier ramfall and snowfall of high mountains, 
their plants and animals are milike those living on the sur- 
rounding lowlands. On lofty mountain flanks in the tem- 
perate zone, hardy cone-bearmg trees usually succeed trees 
that need a milder climate. As the limit of tree growth, or 
the "tree line," is approached only stunted and deformed 
trees survive. Then comes a belt in which the slopes bear 
grass and Alpine flowers. (Alpine is used to refer not only 
to the European Alps, but also to the animals and plants of 
any lofty mountain.) Following this is the lower limit of 
summer snow banks, or the " snow line," above which some 
of the snow of one winter lasts over the following summer, 
thus excluding plant life. It is remai'kable that many plants 
found near the snow line on mountains in the warmer zones 
are also found near sea level in the frigid zone, although 
they are wanting on the low gromid between the two. 



356 



ELEMENTARY PHYSICAL GEOGRAPHY 



Many animals survive in mountains after disappearing 
from the surrounding lower ground. Various kinds of 




Fig. 187. Stunted Trees at the Tree Line on the Slope of Pikes Peak 



ibex (mountain goat) are found on the mountains of 
Eurasia, each range having its own peculiar species. All 
are derived from a common ancestry 
on the intermediate lower lands ; but 
since they have been limited to moun- 
tain homes, the animals in each 
range have varied in their own way, 
independently of the others, and have 
thus come to be unlike. This is a 
remarkable illustration of the effect 
of mountains in keeping their inhab- 
itants apart from the rest of the world; it may be com- 
pared with the effect of isolation on islands. 




Fig. 188. Ibex 



THE DISTRIBUTION OF ORGANIC FORMS 357 

A species of butterfly living on the White mountain 
summits, in New Hampshire, is unlike the species of the 
surrounding lower ground, but resembles those of more 
northern lands. The top of Mt. Katahdin, an isolated 
mountain in northern Maine, possesses a similar butterfly, 
but it varies somewhat from the one on the White moun- 
tains, the variation having taken place since the butterflies 
of the two districts were isolated on their mountam homes. 

203. The Effect of Mountains on their Human Inhab- 
itants. — It has already been stated that the deep valleys 
of lofty mountains have often been used as retreats by the 
people of a nation that has been driven from the neigh- 
boring lower land by the invasion of a stronger nation. 
The following examples may be cited. 

The Basques live in the northern valleys of the Pyrenees, 
near the angle of the Bay of Biscay. They are probably 
descendants of the Iberians, an ancient people who occu- 
pied a large part of Spain and France, from which they 
had been driven by invaders even before Caesar made 
those countries subject to Rome, nearly 2000 years ago. 
The Basque language is the only surviving form of Iberian, 
and is entirely unlike other European languages. 

The Svanetians occupy deep inner valleys in the Cau- 
casus mountains, with difficulty accessible from the outer 
country. They are the descendants of an ancient people 
who occupied a much more extensive territory, from which 
they were driven back to the mountains many centuries 
ago. There ancient customs and a peculiar language are 
preserved ; there the people still live entirely apart from 



358 ELEMENTARY PHYSICAL GEOGRAPHY 

the ways of modern times. Although daring and patri- 
otic, they are ignorant and superstitious. Their wretched 
houses are dark and dirty ; their roads are only rough 
tracks. Arts and industries are of the simplest order ; 
trade is only by barter. 

The people who live in deep valleys among lofty moun- 
tains find life more difficult than do those who live on open 
plains. The difference between the two cases is in large 
part due to the action of gravity on the mountain sides. 
The peculiar dangers of avalanches and landslides are 
directly the result of gravity. The finer Avaste on the 
steep slopes is rapidly washed down by active rivulets. 
The stony soil that remains cannot be easily cultivated, 
and if it is spaded or plowed, much of it will be washed 
away by the next heavy rain. 

The valley floors are narrow, giving little room for fields. 
The streams flow swiftly down their sloping channels ; 
their torrential current is too strong to be navigated ; their 
floods are frequent and destructive. It is difficult to pass 
from one valley over the dividing ridge to the next valley 
because of the labor of climbing up and down the slopes. 
Hence, although mountaineers are active and hardy, they 
are not, as a rule, great travelers or traders. The j)eople of 
one valley know little of those a few score miles away, 
a distance that would be considered a trifle by a horse- 
man on a plain. The people of neighboring valleys are 
often distinguished by slight differences in their common 
lano-uaore. 

During winter mountain valleys may receive a heavy 
snowfall. Then for a season the people and their flocks 



THE DISTRIBUTION OF ORGANIC FORMS 359 

are gathered in the lower villages, living on supplies stored 
up from the previous summer. In summer, when the snows 
are melted from the mountain sides, cattle, sheep, and goats 
are driven up from the valleys to pasture on the grassy 
slopes of the ridges. Hay is carried, often on the backs 
of the mountaineers, down to the villages for winter need. 

204. Life in Deserts. — Climate exerts a powerful con- 
trol over the distribution of life through differences of rain- 
fall. This control is well illustrated by the conditions of 
those regions where rainfall is deficient. Plant and animal 
life is scanty in deserts because of the difficulty of secur- 
ing food and water. The dryness of the soil is unfavorable 
to plant growth. Leaves are small or wanting, for thus 
the loss of water by evaporation from the leaf surfaces is 
diminished. Thorns are commonly developed, like so many 
signs, "keep off," as if to lessen the chance of injury to 
the plant in a region where living is so difficult that every 
aid must be summoned to protect life. 

During long droughts an arid region may seem almost 
free from vegetation. If rain falls, small plants spring up 
everywhere, refreshing the surface with their green color, 
but soon withering away in the succeeding dry period. 
On the desert slopes of Peru, where droughts may last 
four or five years, plants soon spring up after a shower. 
These examples show that the plants of arid regions 
possess great vitality. 

The larger plants of arid regions are thinly scattered, 
leaving much bare surface. There is no striving for space, 
such as commonly occurs in well-watered regions, where 



360 



ELEMENTARY PHYSICAL GEOGRAPHY 



plants of more active growth may crowd out the weaker 
forms. Dry regions seldom produce useful plants. Trees 
are small, and their wood is hard and knotted; they cast 
little shade on the dry, bare ground. The sagebrush, so 

abundant on the arid 
western plains of the 
United States, finds 
no use except as an 
inferior firewood. 

The animals of des- 
erts are generally of 
dull or gray color, not 
easily seen on the bar- 
ren surface. INIany 
of them are fleet in 
movement, like the 
antelope, or of great 
endurance under a 
small supply of food 
and water, like the 
camel. Those which are sluggish are often venomous, 
like the tarantula, the scorpion, and the rattlesnake. 




Fig. 180. The Yucca, a Desert Tree 



205. The People of Deserts. — The human inhabitants of 
arid deserts are few and miserable as compared with the 
more favored races of the world. Their food supply is 
scanty and of little variety. Their arts are primitive, for 
raw materials are of few kinds. They possess strength and 
endurance, without which life would be impossible under 
the difiiculties around them ; they have a keen intelligence 



THE DISTRIBUTIOX OF ORGANIC FORMS 361 

for every advantage that their desert home affords, but 
they cannot rise above a low stage of development. 

Many of the wandering tribes of the Sahara find the 
struggle for existence so severe that they and their 
animals are often on the verge of starvation. They must 
move from place to place to secure food ; hence they do not 
build houses, but live in tents that can be easily carried 
about as they wander from one pasture ground to another. 
As a result of their wandering habits, they have come to 
be excellent horsemen and show great endurance in sur- 
viving the hardships that they must often suffer. But, on 
account of being nearly destitute, they have the habit of 
taking what they want from any passing travelers whom 
they can plunder. They have thus preserved into modern 
times a rude manner of life which must have been universal 
in the early history of mankind, but which has been given 
up in recent centuries by the people of more advanced 
nations, among whom theft is now punished as a crime. 

The Papago Indians of the Sonoran region, south of 
the Gila river (southwestern United States, northwestern 
Mexico), move from place to place with the failing and 
flowing of springs. They are- noted for strength, speed, 
endurance, and abstinence. The Seri Indians, living in 
the desert on the border of the Gulf of California, have no 
horses and are noted as runners. 

206. Oases. — Fixed settlements in desert regions are 
controlled by the presence of water. They are commonly 
made where springs or streams flow upon the open country 
at the base of uplands and mountains; or near the ends of 



362 



ELEMENTARY PHYSICAL GEOGRAPHY 



such streams, where the water can be distributed in irri- 
gating canals; or at points where ground water may be 
found in the nearly dry channels of withered streams. 
Such settlements are called oases in the Sahara, and the 
same name may be used elsewhere. 




Fig. I'.K). El Kaiitara Oasis, Algerian Sahara 

The barrenness of many deserts is due simply to their 
dryness and not to an unfavorable composition of rock or 
soil. Where springs or streams moisten the soil, grass 
and trees may grow naturally. If the surface can be 
irrigated, its productiveness may be increased so as to 
support permanent settlements. 

The contrast between a habitable spot and the surround- 
ing barrenness is so grateful that " an oasis in the desert " 
has come to serve as a poetic figure. But oases are only 
relatively delightful. , Their water supply is often limited 
and impure; their products are few in variety and small 



THE DISTRIBUTION OF ORGAXIC FORMS 363 

in quantity; their industries are primitive; their inhab- 
itants have to suffer the disadvantages of isolation as 
completely as do the people of islands. 

The oasis of Siwa, in the Sahara, 350 miles west of 
Cairo, " the first halting place on the great desert highroad 
to the west," is still little changed from its condition in 
ancient times. Seclusion seems to have bred mistrust, for 
strangers are looked on as intruders. They and their 
modern ways of doing things are unwelcome. 

It sometimes happens that a river rising in well-watered 
regions flows across a desert on its way to the sea. If the 
river has developed an open and accessible valley, nearly 
all the population of the region is gathered on its flood 
plain. 

The most famous river of this kind is the Nile, which 
flows 1000 miles through the desert without receiving a 
branch, except a few small wet-weather streams. Its flood 
plain, several hundred feet below the desert uplands 
that inclose it, is about 500 miles long and from 5 to 15 
miles wide, broadening on the delta to over 100 miles. 
Here most of the millions of Egyptians dwell. Their 
resources are almost wholly agricultural and, as such, 
depend on the annual inundation of the Nile, caused by 
the northward movement of the belt of equatorial rains 
over the upper branches of the river in summer. The flood 
begins in June, usually rising twenty-five feet or more at 
Cairo in late summer or early autumn. For thousands of 
years the fertility of the flood plain has been maintained 
by the annual additions of river silt, estimated to amount 
to four and a half inches a century. Still better use of 



364 ELEMENTARY PHYSICAL GEOGRAPHY 

natural conditions is about to be made by building a strong 
dam across the Nile on a reef of rocks that forms the first 
cataract, at Assouan, and thus storing in a reservoir a 
large volume of water for irrigation that would otherwise 
run to the sea unused. 

207. Geographical Factors in the Life of Civilized Peoples. 

— It has already been shown that the simplest examples 
of the relations of man and nature are to be found in the 
life of savages, who know few arts and have little inter- 
course with other peoples and who are therefore directly 
dependent on the simplest home products. What can you 
say in this connection about the natives of coral islands ? 

Civilized nations offer much more complicated exam- 
ples of these relations. Here the people are engaged in 
agriculture, manufactures, and commerce. Arts and trades 
are highly developed ; the products of many parts of the 
world are gathered and skillfully manufactured into a 
great variety of articles for use at home and abroad. It 
might at first seem as if such a people had overcome 
geographical controls; but closer study will always show 
that they are influenced by them on all sides, and that 
their progress is less dependent on overcoming geograph- 
ical obstacles than on taking advantage of geographical aids. 

In savage tribes there are so few things to do that every 
man is well practiced in nearly all the duties of a man's 
life. In civilized nations man's work has become greatly 
diversified, and " a jack of all trades is master of none." 
Many occupations are immediately dependent on geograpli- 
ical factors, and the skill needed in them is so great that 



THE DISTRIBUTION OF ORGANIC FORMS 365 

few persons are successful in more than one. A miner, a 
farmer, a sailor, each knows his own work but would be 
at a loss in the work of his neighbors. 

Some of the ways in which men gain a living require a 
very close acquaintance with geographical details. A river 
pilot must know all the bends and shoals in a river channel 
and must learn how they are changed by the action of the 
river in scouring away or building up the banks and in 
sweeping waste along the bed. 

Certain peculiar occupations. are dependent on a variety 
of geographical conditions. For example, in stormy 
weather the schooners that sail between our Atlantic 
ports sometimes anchor in shallow water near the shore. 
In very severe storms the cables may break and the 
anchors are then lost. But anchors are valuable; hence 
men, known as " anchor draggers," make a business of 
parching for them. They sail in pairs and drag a strong 
rope between their vessels over the sea bottom in fre- 
quented anchorage grounds, and they know their curious 
trade so well that they make a living by selling the 
anchors that they find. Can you give some other examples 
of this kind ? 

A member of an isolated savage tribe depends for food, 
clothing, weapons, and dwelling upon what he finds close 
to his home ; if work is needed in building a hut, in secur- 
ing food, in making clothing or weapons, it is usually done 
by each family separately. There are no mills where flour 
is ground wholesale; there are no factories where cloth is 
woven; there are no shops where household supplies can 
be bought. 



366 ELEMENTARY PHYSICAL GEOGRAPHY 

In a civilized country a family may occupy a house which 
they had no share in building and which required for its 
construction the labor of many men in many trades, — 
masons, carpenters, plumbers, plasterers, and painters. 
The materials used in building the house may have been 
brought from hundreds of miles away. The stone for the 
foundation, the lime for mortar, the cement for the cellar 
floor, the clay for bricks in the chimney, the plaster for the 
walls are products of quarries and pits in different dis- 
tricts. The beams for the frame, the boards for the walls 
and floors, the shingles for the roof have probably come 
from different forests. 

The furniture may be made from various kinds of wood, 
metal, and cloth, gathered from far and wide, put together 
in great factories, and distributed for sale. The carpets 
are very likely spun from wool from the pampas of South 
America. The iron in the kitchen utensils probably comes 
from iron ore in the old worn-down mountain region west 
of Lake Superior, smelted with coal from the dissected 
plateau of western Pennsylvania ; the tin of tinware prob- 
ably comes from the Malay peninsula southeast of Asia. 
The crockery may be from the lowland clay belt of the 
New Jersey coastal plain. 

The daily food may include bread from flour ground by 
the water power of a displaced river in Minnesota from 
wheat grown in the rich drift soils of the northern prairies 
or in the deep- weathered soils of the lava plains of Washing- 
ton, beef from the cattle ranches of the Great plains, tea 
from China, coffee from Brazil, sugar from Cuba, and salt 
from New York. The production of all these materials 



THE DISTRTBUTIOX OF ORGANIC FORMS 367 

depends on such geographical factors as rock, soil, and 
climate. Their preparation has required skilled labor of 
many kinds, in which natural forces are usually employed. 
Their transportation has been over lands and seas, along 
routes influenced by geographical conditions at every turn. 
The family for whose comfort all these threads of activity 
meet in a single house may be that of a typesetter, skillful 
in his own work, but unprepared to take part in any one 
of the many arts- and trades on which his home comforts 
depend. He would be almost helpless alone; but if lie 
and every one else works faithfully and well, each one doing 
his chosen task to the best of his ability, the whole nation 
thrives. Yet civilized life is so complicated that, until 
attention is directed to its separate items, one might fail to 
notice how largely they are determined by geographical 
controls. 

How many kinds of materials can you name that were used in 
the house you live in ? How many of these materials can you trace 
back to their sources ? From how many different states or countries 
did they come ? What natural forces have been employed in pre- 
paring the materials for use ? How have the materials been brought 
to their place of use? Similar questions may be asked concerning 
furniture, food, and clothing. 

208. The Influence of Geographical Factors on History. — 

The progress of history has been repeatedly influenced by 
geographical factors. It is fortunate for the modern his- 
tory of America that the Atlantic is narrower than the 
Pacific; it is chiefly for this reason that the New World 
has been peopled by emigrants from the leading races in the 
western part of Europe, instead of from the less advanced 



368 ELEMENTARY PHYSICAL CtEOGRAPHY 

peoples of eastern Asia. The eastern coast of North America 
has abundant harbors where the newcomers found safe 
refuge for their vessels. All tlie early settlements, many 
of which have now become important seaboard cities^ were 
located on these protected embayments of the coast line; 
none of them were established on exposed headlands. 

The boundaries of the several colonies founded by the 
immigrants were in most cases established with regard to 
the harbors on which the more important settlements had 
been made. The small size of several of the colonies, and 
of the states that now i-epresent them, was determined by 
the occurrence of bays or rivers to the 'west, where other 
colonies were formed. Rhode Island, founded by settle- 
ments on the drowned valley known as Narragansett bay, 
was limited on the west by the colony which took posses- 
sion of the lower Connecticut valley; and Connecticut was 
in turn limited by New York, whose inland growth from 
its excellent harbor was guided northward by the drowned 
valley of the Hudson. New Jersey was cut off from west- 
ward growth by Pennsylvania, whose chief city was estab- 
lished near the head of the drowned lower part of a valley, 
known as Delaware bay. The small state of Delaware was 
limited on the west by Maryland, founded on Chesapeake 
bay, the drowned lower valley of the Susquehanna ; and 
Maryland was in turn limited by Virginia, to whose terri- 
tory the Potomac embayment of the partly drowned coastal 
plain gave easy access west of Maryland, Farther south 
there are no important bays or rivers along the Atlantic 
coast with a north and south trend, and there are no more 
small states. 



THE DISTRIBUTION OF ORGANIC FORMS 369 

JNIentiou some geographical factors on which the importance of 
New York city depends; of Chicago; of San Francisco. Mention 
some factors on which the small population of the Appalachian 
highlands and the great population of the i>rairie states depend. 

Success in warfare lias often been influenced directly or 
indirectly by geographical factors. The size of an army is 
largely the consequence of such factors as the area, form, 
climate, and fertility of the country to which it belongs; 
the strength of the less civilized nations has therefore often 
been measured by the number of their warriors. The 
character of soldiers is largely dependent on the habits of 
the community from which they are enlisted. Regiments 
of infantry recruited from among mountaineers have always 
been famed as fighting men, for they have learned endur- 
ance and courage from the severe conditions of life in 
their rugged homes. Regiments of cavalry recruited from 
dwellers on grassy plains are famous as "rough-riders," 
whether they are Russian Cossacks or American cowboys ; 
their skill and endurance as horsemen are a natural result 
of habits developed in an open country of large distances, 
where riding is as appropriate a means of going about as 
walking is in a mountainous district. 

What exami)le can you give of a people whose home favored their 
becoming skillful sailors, and who thereby became invaders and con- 
querors of other lands? (See page 321.) 

The fate of battle fields has been many a time determined 
by the arrangement of high and low ground; hence an 
intimate knowledge of land forms and of local geography 
is of great importance to military commanders. During 
the recent war in South Africa the Boers, having an 



370 ELEMENTARY PHYSICAL GEOGUArHY 

accurate acquaintance with their country, often occupied 
the crests of hills, and thus gained advantage over the 
British soldiers, who had to make attack while climbing up 
a slope from lower ground. 

What can you learn about the Spartans at Thermopylse ? What 
can you tell of Braddock's defeat V 

209. Geographical Factors favoring the Development of 
Great Britain. — The progress and prosperity of a nation 
are even more dependent in peace than in war on the 
advantage that its people have learned to take of their 
surroundings. 

West of continental Europe, in the latitude of Labrador, 
there is an island whose climate is remarkably mild, because 
it is on the leeward side of an ocean across which the sur- 
face waters and the winds move obliquely poleward from 
warmer latitudes. The island is therefore fertile and has 
long been noted for its agricultural products. The narrow 
strait by which it is separated from the continent has served 
as a natural fortification against the armies of neighboring 
nations ; nearly a thousand years have passed since the 
island has been successfully invaded. It has rich mines of 
coal and iron, and these natural products have been skill- 
fully used in promoting manufactures of the most diversi- 
fied kinds. It has excellent harbors, and many of its people 
have therefore been fishermen and sailors ; its navigators have 
crossed the most distant oceans and have developed a world- 
wide commerce. As the population of the island increased 
under all these favoring conditions, many of its people 
emigrated to the new lands discovered by its explorers 



THE DISTRIBUTION OF ORGANIC FOiaiS 371 

and founded colonies in them; and to-day the sun never sets 
on the island's possessions. The empire thus established 
is the most widespread that the world has ever seen. 

210. The United States. — A more modern instance of 
the dependence of prosperity on geographical elements is 
seen in the rapid growth, as a world power, of a young 
nation whose center of population now lies in a region 
where the winter is so severe that provision must be made 
for it, yet where the summer warms a fertile soil from 
which industry secures provision in plenty and to spare ; 
where open plains and great rivers made it easy for new 
settlers, to enter the country, and where the small relief of 
the surface favored the construction of the numerous rail- 
roads demanded by growing traffic, yet where the variety 
of form is sufficient to promote diversified industries; where 
the products of forest and mine are added to those of the 
farm, and where these excellent conditions are spread over 
so extensive an area that abundant opportunity is offered 
for a vast population. 

Yet these favoring conditions have not been in them- 
selves sufficient for the growth of a powerful nation. The 
aboriginal inhabitants of this great land were savages who 
did not know how to develop its riches. The entire 
teil'itory remained a wilderness until it was entered by the 
descendants of a race that had, by long occupation of 
another highly favored region, gained a leading position 
among the peoples of the Old World. 

But these members of the leading race of the Old World 
would not have left their homes for a new country, however 



372 ELEMENTARY PHYSICAL GEOGRAPHY 

favorable its geographical features, if its government 
had been tyrannical and oppressive. It is therefore not 
local geographical factors alone that have so soon given 
this young nation a giant's strength, but three highly 
favoring conditions combined: a land well situated, of 
great extent, and rich in many forms of natural wealth ; 
numerous immigrants from the leading race of the Old 
World; and a liberal form of government under which 
the highest opportunity is open to every citizen. Let us 
remember that " it is excellent to have a giant's strength, 
but tyrannous to use it like a giant." 

QUESTIONS 

Sec. 191. How have geographical conditions affected man's prog- 
ress ? Illustrate this by the use that has been made of the winds ; 
of waterfalls ; of flood plains ; of terrestrial magnetism ; of coal and 
iron. Give some examples of the effects of geographical conditions 
on the distribution of plants ; of animals ; on man's way of living. 

192. How is it known that the earth has long been inliabited? 
What barriers prevent the spread of organic forms? Contrast the 
spreading of plants having heavy and light seeds. In what way do 
corals and mussels resemble certain land plants? How have free- 
moving animals been distributed ? Contrast the distribution of 
walking and of flying birds. How is the rotation of the earth 
shown to be a factor in the distribution of certain birds ? 

193. How is the number of plants or animals in a region limited? 
How does man sometimes cause a change in these numbers? Why 
do plants and animals tend to increase in number? Why does 
their number not increase ? Explain the phrases " struggle for 
existence " ; " survival of the fittest " ; " natural selection." Upon 
what does the chance of sm-vival depend? Illustrate by examples 
from sea animals. What effects follow from the illumination of 



THE DISTRIBUTION OF ORGANIC FORMS 373 

the earth from the sky? Give some examples of protection gained 
by living in out-of-the-way places. 

194. Compare ancient and modern plants and animals. How 
have variations in plants and animals been caused? Illustrate by 
changes in a coastal plain ; in mountains ; in climate. 

195. Name one of the strongest contrasts of geographical con- 
ditions. What proof can be given of the great age of the continents 
and oceans ? What consequences follow from the greater density of 
water than of air ? Contrast the conditions of the sea bottom with 
those of the lands. State some results of these contrasted conditions. 
What can you tell about the warm-blooded animals of the sea? 
^Vhy are they believed to be descended from land animals ? Give 
examples of the remarkable instincts of certain land animals. 

196. How are the several continents arranged ? Over what region 
are similar land plants and animals found ? Name some examples. 
Name some of the animals and plants of the lower northern lati- 
tudes in the Old and in the New Worlds. What is inferred from 
their differences ? Name some of the animals of the three southern 
continents. Why are mammals not found in Australia ? Name some 
animals and plants native to one part of the woi'ld and thriving in 
another part. 

197. How has mankind been divided into races? In what ways 
do the races differ ? Describe the races of Eurasia ; of America ; 
of Africa ; of Australia. How are the races now distributed ? 

198. What forms of life are found on continental islands ? What 
is inferred from this? How have these islands been separated from 
the mainland ? Illustrate by the cassowaries ; by mammals and 
marsupials on the islands between Asia and Australia. What forms 
are found on oceanic islands? What is the origin of the names 
Azores and Galapagos? 

199. How does climate control the distribution of plants? Illus- 
trate by the palm (see Figure 112), by cotton, corn, and wheat. What 
is the vegetation of the northern treeless belt? How does climate 
control the distribution of animals ? Give examples. How does the 



374 ELEMENTARY PHYSICAL GEOGRAPHY 

distribution of plants control that of animals? Give examples froiri 
North and South America. 

200. Name some direct and some indirect effects of climate on 
man. Why are climatic influences more apparent on savage tribes 
than on civilized peoples? Describe the conditions prevailing in 
the forests of equatorial Africa. Describe the life of the Dwarfs of 
these forests. Explain the relation between their life and their 
environment. Do the same for Greenland and the Eskimos. What 
general truth do these examples illustrate ? 

201. Give an example of the effects of the change of seasons on 
plants in the torrid zone ; in the north temperate zone. What are 
annxial plants? Name several ways in which animals survive the 
winter. How does the oblique position of the earth's axis affect the 
life of plants and animals ? How does change of season affect man's 
way of living ? Give examples from the Caspian steppes ; from 
Algeria. Of what advantage has winter been in the development 
of civilization? 

202. How does climate vary on mountains ? Desci'ibe the changes 
of vegetation seen on ascending a mountain. AV'hat is the tree line? 
the snow line? What are Alpine plants? In what lowland region 
are the plants of high mountains found? What may be learned 
from the distribution of the ibex? Give a similar example from 
the mountains of New England. 

203 . How have mountain valleys been used by defeated peoples ? 
Give an example from the Pyrenees ; from the Caucasus. Why is 
life more difficult in mountains than on plains ? Name some of the 
customs of mountaineers. 

204. Mention some of the features of desert vegetation. What 
is the effect of rain in a desert ? Describe the conditions of gi-owth 
of desert plants. What can you say of desert animals ? 

205. Describe the inhabitants of deserts ; the conditions of life 
in the Sahara ; the Indians of the Sonoran region. 

206. What are oases? What controls their location ? Why are 
deserts barren? Describe the oasis of Siwa. Describe the Nile 



THE DISTRIBUTION OF ORGANIC FORMS 375 

valley. To what are its floods due ? Of what value are they ? How 
is their value to be increased? 

207. Where are the simplest examples of the relation of man 
and nature found? Why are civilized people less dependent than 
savages on natural conditions? How have civilized people been 
affected by geographical conditions? Give examples. What are 
anchor draggers? Show that savages are dependent on immediate 
surroundings and on individual work. Show that civilized people 
are often dependent on distant su^jplies and on the work of many 
men in many trades. 

208. What geographical factors have affected the historical 
"levelopment of North America? How were the boundaries of the 
smaller northeastern states determined? Show that the character 
of soldiers and their success in warfare are dependent on geographical 
conditions. 

209. 210. Describe the geographical factors that have favored 
the development of Great Britain. What favorable factors are 
found in the United States? What other factors have contributed 
to our national growth ? 



APPENDIX 



EEFEKEXCES FOR SUPPLEMENTARY READING 

The titles in the following list have been selected with especial 
refei-ence to their accessibility in public libraries. Mention is made 
of the publications of the U. S. Geological Survey because of their 
great A^alue to the geographer as well as of their wide distribution. 
Numbers preceding certain refei'ences indicate the page of this book 
to which the articles cited pertain. 

GENERAL REFERENCES 

Gannett, The United States, Stanford's Compendium of Geography, 
Edward Stanford, 1898. 

The International Geography. D. Appleton & Co., 1899. 

Annual Reports, Bulletins, Monographs, and Geological Folios of 
the U. S. Geological Survey. Some of the more geographical 
essays are referred to below (abbrev., G. S. Ann. Rep., etc.). 

The following geographical periodicals contain much material 
serviceable in teaching : 

National Geographic Magazine, Washington, D. C. (abbrev., N. G. M.). 
Bulletin of the American Geographical Society. New York (B. A. G. S.). 
Journal of School Geography, Lancaster, Pa. (-F. S. G.). 
Bulletin of the American Bureau of Geography, ^Vinona, Minn. 
(B. A. B. G.). 

(The two preceding periodicals are united, since .January, 1902, under the 
title, The Journal of Geography .) 

Geographical Journal, London (G. J.). 
Scottish Geographical Magazine, Edinburgh (S. G. M.). 

377 



378 ELEMENTARY PHYSICAL GEOGRAPHY 

Platt, The, Better Books in School Geography, J. S. G., II, '98, 181. 

(All the books mentioned in the above article would be found serviceable 
in school libraries.) 

Mill, Hints to Teachers and Students on the Choice of Geographical 

Books. Longmans, Green & Co. 
Davis, The Equipment of a Geographical Laboratory. J. S. G., II, 

'98, 170. 
Cornish, Laboratory Work in Elementary Physiogi-aphy, J. S. G., 

I, '97, 172, 204. 
National Geographic Monographs, American Book Co., 1895 

(N. G. Mon.). 
Preliminary Report of Committee on Physical Geography of N. E. A. ; 

J. S. G., II, '98, 248. 



CHAPTER L THE EARTH AS A GLOBE 

Young, Astronomy. Ginn & Company, 1888. 

Todd, Astronomy. American Book Co., 1897. 

ScHOTT, The Earth's Shape and Size, N. G. M., XII, '01, 36. 

CHAPTER II. THE ATMOSPHERE 

Waldo, Elementary Meteorology. American Book Co., 1896. 

Davis, Elementary Meteorology. Ginn & Company, 1894. 

Jameson, Elementary Meteorology, J. S. G., II, '98, 2. 

Greely, American Weather. Dodd, M- a 1 & Co., 1888. 

Ward, Practical Exercises in Elementary Meteorology. Ginn & 

Company, 1899. 
Ward, Equipment of a INIeteorological Laboratory. J. S. G., Ill, 

'99, 241. 
Bartholomew, Physical Atlas, Vol. TTI, Meteorology. Lippincott. 

PAGE 

63. Illustrated Cloud Forms, U. S. Hydrographic Office, Washing- 
ton, D.C. 

67. Gakkiott. West Indian Hurricanes, X. G. M., X, '99, 17, 343 ; 
XI, '00, 384. 



APPENDIX 379 

PAGE 

72. (treely, Rainfall Types of the United States, N. G. M., Y, 

'93, 45. 
72. Harrington, Rainfall of the United States, U. S. Weather 

Bureau, Bulletin C, 1894. 
72. fxANNETT, Redwood Forest of the Pacific Coast, N. G. M., X, 

'99, 145. 
84. Davis, The Temperate Zones, J. S. G., I, '97, 139. 
84. Ward, Climatic Control of Occupations in Chile, J. S. G., I, 

'97, 289. 
87. Davis, Practical Exercises in Geography, N. G. M., XI, '00, 62. 



CHAPTER III. THE OCEAN 

Thomson, The Depths of the Sea. Macmillan & Co., 1874. 
Thomson, The Voyage of the Challenger : The Atlantic. Macmillan 

& Co., 1877. 
SiGSBEE, Deep Sea Sounding and Dredging, Washington, 1880. 
Tanner, Deep Sea Exploration, U. S. Fish Commission,Washington. 
Agassiz, Three Cruises of the Blake, Cambridge, 1888. 
Monthly Pilot Charts of the North Atlantic and the North Pacific 

Oceans, U. S. Hydrographic Office, Washington. 
Semple, The Atlantic and Pacific Oceans, J. S. G., Ill, '99, 121, 172. 

PAGE 

109. Davis, AVaves and Tides, J. S. G., II, '98, 122. 

113, Scidmore, Earthquake Wave, Japan, N. G. M., YII, '95, 285. 

114. Davis, Winds and Ocean Currents, S. G. M., XIII, '97, 55, 

and J. S. G., II, '98, 16. 

118. PiLLSBURY, The Gulf Stream, Ann. Rep. U. S. Coast Survey, 

1890. 

119. Tide Tables, published annually by I'. S. Coast Survey. 

121. Jefferson, Atlantic Estuarine Tides, N. G. M., IX, '98, 400 ; 
also 497. 



380 ELEMENTARY PHYSICAL GEOGRAPHY 



CHAPTER IV. THE LANDS 

Shaler, Aspects of the Earth. Charles Scribner's Sons, 1889. 

J. Geikie, Earth Sculpture. G. P. Putnam's Sons. 

Text-books on Elementary Geology, by Dana, Geikie, Leconte, 

Scott, Tarr, and Brigham. 
Shaler, Origin and Nature of Soils, G. S. 12th Ann. Rep., Pt. I, 219. 
Patterson, Work of the Water Giant, J. S. G., Ill, '99, 5. 



CHAPTER V. PLAINS AND PLATEAUS 

PAGE 

142. Davis, Description of the Harvard Geographical Models, pub- 
lished by the Boston Society of Natural History, Berkeley 
Street, Boston. Figures 60, 62, and 104 are taken from 
these models. 

148. Glenn, South Carolina, J. S. G., II, '98, 9, 85. 

149. Cobb, North Carolina, J. S. G., I, '97, 256, 300. 
156. Abbe, Maryland, B. A. B. G., I, '00, 151, 242. 

156. McGee, Chesapeake Bay, G. S. 7th Ann. Rep., 548. 

157. McGee (Fall Line), G. S. 12th Ann. Rep., 360. 

158. Hatcher, Patagonia, N. G. M., XL '00, 41. 

158. Johnson, High Plains, N. G. M., IX, '98, 493 ; G. S. 21st Ann. 

Rep., 601. 

159. Fenneman, Climate of the Great Plains, J. S. G., Ill, '99, 1, 46. 
161. Collie, Physiography of Wisconsin, B. A. B. G., II, '01, 270. 
166. Powell, Exploration of the Colorado River of the West, 

Washington, 1875. See pp. 98-102, 130, 131. 

166. Powell, Canyons of the Colorado. Flood & Vincent, Mead- 
ville, Pa. 

166. DuTTON, Colorado Canyon, G. S. 2d Ann. Rep., 40; G. S. 
Monogr. II. 

168. Campbell and Mendenhall (Plateau of West Virginia), 
G. S. 17th Ann. Rep., 480. 

168. Roosevelt, Winning of the West, I, 101 ; III, 13. G. P. Put- 
nam's Sons, 1894. 



APPENDIX 381 

PAGE 

168. Semple, Influence of the Appalachian Barrier upon Colonial 

History, J. S. G., I, '97, 3:3. 
172. Hodge, The Enchanted Mesa, N. G. M., VIII, '97, 273. 

CHAPTER VI. MOUNTAINS 

178. Russell, Southern Oregon, G. 8. 4th Ann. Rep., 435. 

181. Russell, Mountains of Nevada, G. S. Monogr. XI, 38. 

185. Fay, Canadian Alps, J. S. G., I, '97, 160. 

185. WiLLCOX, Canadian Rockies, J. S. G., I, '97, 293 ; also N. G. M., 
X, '99, 113. 

197. Lubbock, Scenery of Switzerland. Macniillan & Co., 1896 
(p. 124). 

201. Milne, Earthquakes. D. Appleton & Co., 1883. 

205. Willis, Round about Asheville, N.C., N. G. M., I, '89, 291. 

205. A. Geikie, Scenery of Scotland, 2d ed. (chapters on High- 
lands). Macmillan & Co., 1887. 

205. Herbertson, Geography of Scotland, J. S. G., II, '98, 161. 

206. McGee, Geographical History of the Piedmont Plateau, 

N. G. M., YII, '96, 261. 
206. Keith, Piedmont Plateau, G. S. 14th Ann. Rep., 366. 
208. Davis, Southern New England, N. G. Mon. 
208. Davis, Geographical Illustrations (Southern New England), 

published by Harvard University, Cambridge, Mass. 
210. Willis, Northern Appalachians, N. G. i\Ion. See also 

B. A. B. G., I, '00, 342-355. 
210. Hayes, Southern Appalachians, N. G. Mon. 
210. Hayes, Physiography of the Chattanooga District, G. S. 19th 

Ann. Rep., Pt. II, 1. 
210. Davis, Rivers and Valleys of Pennsylvania, N. G. M., I, 183. 

CHAPTER VII. VOLCANOES 

Russell, Volcanoes of North America. Macmillan, 1897. 
Dana, Characteristics of Volcanoes. Dodd, Mead & Co., 1890. 



382 ELEMENTARY PHYSICAL GEOGRAPHY 

JuDD, Volcanoes. D. Appleton & Co., 1881. 
Dodge, Volcanoes, J. S. G., I, '97, 179 ; IV, '00, 350. 

PAGE 

218. Lyell, Principles of Geology (Monte Nuovo, I, 607; JoruUo, 

I, 58.5). -D. Appleton & Co., 1872. 

219. DiLLER, A Late Volcanic Eruption in Northern California, 

G. S. Bull. No. 79. 
221. Phillips, Vesuvius. Macmillan & Co., 1869. 

221. Milne, Earthquakes. D. Appleton & Co., 1883. 

222. Diller, Crater Lake, N. G. M., VIII, 33. 
222. Diller, Crater Lake, J. S. G., I, '97, 266. 

226. Moore, The Active Volcanoes North of Kivu (Central Africa), 

G. J., XVIT, '01, 11. 

227. DuTTON (Lava Flows), G. S. Monogr. II. 

227. DuTTON, Hawaiian Volcanoes, G. S. 4th Ann. Rep., 81. 
229. Diller, Mt. Shasta, N. G. Mon. See also B. A. B. G., I, '00, 260. 
231. Hayes, Physiography of the Nicaragua Canal Route, N. G. M., 
X, '99, 233. 



CHAPTER VIII. RIVERS AND VALLEYS 

Russell, Rivers of North America. G. P. Putnam's Sons, 1898. 

PAGE 

235. Hovey, Celebrated American Caverns. Clarke, Cincinnati. 

235. Hovey, Mammoth Cave, J. S. G., I, '97, 133. 

236. Walcott, Natural Bridge of Virginia, N. G. M., V, '93, 59. 

238. Chamberlin, Artesian AVells, G. S. 5th Ann. Rep., 125. 

239. Weed, Hot Springs, G. S. 9th Ann. Rep., 613. 
247. Bell, The Labrador Peninsula, S. G. M., XI, 335. 
251. Gilbert, Niagara, N. G. Mon. 

260. Davis, Seine, Meuse, and Moselle, N. G. M., VII, '97, 189, 228. 
264. Gannett, The Flood of April, 1897, in the Lower Mississippi, 

S. G. M., XIII, '97, 419. 
266. Fairbanks, Physiography of California, B. A. B. G., IT, '01, 

232, 329. 



APPENDIX 383 

CHAPTER IX. DESERTS AND GLACIERS 

I'AGE 

i'78. Marbut, Missouri, J. S. G., I, '97, 110, 1-14. 

280. Platt, The Sahara, J. S. G., IV, '00, 255. 

282. King, Geological Survey, 40th Parallel, AVashington, I, 400, 

484 ; II, 470. 

282. McGek, Seriland, N. G. M., VII, '97, 125. 

284. Russp:ll, Past and Present Lakes of Nevada, N. G. Mon. 

286. Davis, A Temporary Sahara, J. S. G., IV, '00, 171. 

288. Gilbert, Lake Bonneville, G. S. 2d Ann. Rep., 169. 

288. Gilbert, Lake Bonneville, G. S. Monogr. I. 

289. Russell, Lake Lahontan, G. S. 3d Ann. Rep., 195. 

290. Holder, A Remarkable Salt Deposit, N. G. M., XII, '01, 391. 
290. Russell, Glaciers of North America. Ginn & Company, 1897. 
290. Shaler and Davis, Glaciers. Houghton, Mifflin & Co., 1881. 
290. Tyndall, Forms of Water. D. Appleton & Co., 1872. 

290. J. Geikie, Great Ice Age, 3d ed. D. Appleton & Co., 1895. 

290. Wright, Ice Age in North America. D. Appleton & Co., 1890. 

291. Arctowski, Exploration of Antarctic Lands, G. J., XVII, 

'01, 50. 
291. Nansen, First Crossing of Greenland, 1890. Longmans, 
Green & Co., 1890. 

291. Peary, Northward over the Great Ice. Frederick A. Stokes 

Co., 1898. 

292. Russell, Glaciers of Alaska, G. S. 13th Ann. Rep., 7. 
292. Russell, Mt. St. Elias, Alaska, N. G. M., Ill, 53. 
292. Reid, Muir Glacier, Alaska, N. G. M., IV, 19. 

292. Reid, Glacier Bay and its Glaciers, G. S. 16th Ann. Rep., Pt. I, 

415. 
292. Russell, Existing Glaciers of the United States, G. S. 5th 

Ann. Rep., 303. 
295. Russell, Mono Lake Region, G. S. 8th Ann. Rep., Pt. I, 321. 
295. Bell, The Labrador Peninsula, S. G. M., XI, 335. 
295. A. Geikie, Scenery of Scotland, 2d ed. (chapters on Glacial 

Action). Macmillan & Co., 1887. 



384 ELEMENTARY PHYSICAL GEOGRAPHY 

PAGE 

295. Russell, Geography of the Laiirentian Basin, B. A. G. S., 

XXX, '98, 226. 

296. McGee, Drift Plains of Iowa, G. S. 11th Ann. Rep., 393. 
296. Taylor, Studies in Indiana Geography, Terre Haute, 1897. 

(" Short History of the Great Lakes.") 

296. Gilbert, Modification of Great Lakes by Earth Movement, 

N. G. M., YIII, 233. 

297. Chamjberlin, Rock Scorings, G. S. 7th Ann. Rep., 155. 
297. Chamberlin, Terminal Moraines, G. S. 3d Ann. Rep., 295, 
297. Todd, Terminal Moraines in Dakota, G. S. Bull. No. IM, 

16. 
297. Dryer, Studies in Indiana Geography, Terre Haute, 1897. 

The Morainic Lakes of Indiana. 
297. Leverett, The Illinois Glacial Lobe, G. S. Mon., XXXVIIL 

299. Upham, Glacial Lake Agassiz, G. S. Monogr. XXV. 

300. Gannett, Lake Chelan, N. G. M., IX, '98, 417. 

300. Tarr, Lakes and Swamps of New York, B. A. G. S., XXXI, 
'99, 1. 



CHAPTER X. SHORE LINES 

304. Shaler, Sea and Land. Charles Scribner's Sons, 1894. 

308. Shaler, Seacoast Swamps of Eastern United States, G. S. 

6th Ann. Rep., 93. 

308. Shaler, Beaches and Tidal Marshes, N. G. Mon. 

310. Gilbert, Features of Lake Shoi'es, G. S. 5th Ann. Rep., 76. 

311. Shaler, Natural History of Harbors, G. S. 13th Ann. Rep., 93. 
317. A. Geikie, Scenery of Scotland, 2d ed. (chapter on Shore 

Features). Macmillan & Co., 1887. 
324. Darwin, Coral Reefs. D. Appleton & Co., 1889. 
324. Dana, Corals and Coral Islands. Dodd, Mead & Co., 1890. 
324. A. Agassiz, Letter in Am. Journ. Science, Feb., 1898. 



APPENDIX 385 



CHAPTER XI. DISTRIBUTION OF PLANTS, ANIMALS, 
AND MAN 

PAGE 

333. Hkilpkin, Distribution of Animals. D. Appleton & Co., 1886. 
333. Beddard, Zoogeography. University Press, Cambridge, 1895. 
333. MacMillan, Geographical Distribution of Plants, J. S. G., 
April, '97. 

345. BuiNTON, Races and Peoples. 

346. Wallace, Island Life. Macmillan & Co., 1891. 

347. Wallace, Travels in the INIalay Archipelago. Macmillan 
* & Co., 9th ed. 

348. Merriam, Geographical Distribution of Terrestrial Animals 

and Plants, N. G. M., VI, 229. 
355. Gannett, The Timber Line, B. A. G. S., XXXI, '99, 118. 
363. Jenxings-Bramley, A Journey to Siwa, G. J., X, '97, 597. 



386 ELEMENTARY PHYSICAL GEOGRAPHY 



REFEEEXCES FOR MAPS 

The following list of map sheets, selected chiefly from those pub- 
lished by the U. S. Geological Survey and the U. S. Coast and Geo- 
detic Survey, will be found of service in illustrating various examples 
of land forms referred to in Chapters V to X. Complete lists of maps 
published by these Surveys can be had, free of charge, on application. 
The sheets here named might be supplemented by many others in 
illustration of special localities. Some account of the cost and of the 
method of ordering and using the maps is given in the Journal of 
School GeogTaphy, September, 1897, and October, 1898. Coast Sur- 
vey maps are here marked " C. S." The others, unless specially des- 
ignated, are published by the Geological Survey. Numbers preceding 
tlie names indicate the pages of this book to which the maps refer. 

CHAPTER V. PLAINS AND PLATEAUS 

I'AGE 

1.52. Relief Map of New Jersey, published by the State Geological 

Survey, Trenton, N.J. ; price, 25 cents. 
154. Nomini, Md. 
159. Topographic Atlas of the United States, folio 1, Physiogi-aphic 

Types, Pis. I-III. 
164. Mt. Trumbull, Diamond Creek, Ariz. 
168. Kanawha Falls, Nicholas, W. Va. 
172. Watrous, Corazon, N.M.; Abilene, Brownwood, Tex. 
174. Mt. Trumbull, Kaibab, Echo Cliffs, Ariz. 

CHAPTER VI. MOUNTAINS 

181. Disaster, Nev. ; Altm-as, Cal. 
186. Platte Canyon, Huerfano Park, Col. 
204. Asheville, Mt. Mitchell, Pisgah, N.C. 

207. Atlanta, Ga. (Stone mountain is a fine example of a monad- 
nock on the uplands of Georgia.) 



APPENDIX 387 

PAGE 

208. Chesterfield, Granville, Mass.; "Winsted, Derby, Bridgeport, 
Conn. 

210. Harrisburg, Hunimelstown, Lykens, Pa. 

211. C. S. No. 710. 



CHAPTER VII. VOLCANOES 

222. Crater Lake (special sheet), Oregon. 

230. Shasta, Cal. ; San Francisco Mountain, Ariz. 



CHAPTER VIII. RIVERS AND VALLEYS 

247. Citra, Fla. 

251. Niagara Falls (special map). 

256. Mesa de Maya, Col. 

261. Donaldsonville, La. 

264. 8-Sheet Map of the Alluvial Valley of the Mississippi River, 

published by the Mississippi River Commission, St. Louis, Mo. 
264. Preliminary Maps of the Mississippi River, published by the 

Mississippi River Commission, St. Louis, Mo. Edition of 

1900. 
268. C. S. No. 194, Mississippi Delta. 
271. Versailles, Tuscumbia, Mo. 
273. Delaware Water Gap, Pa. ; Harpers Feriy, Va. 



CHAPTER IX. DESERTS AND GLACIERS 

281. Disaster, Granite Range, Long Valley, Nev. 

299. Oconomowoc, Sun Prairie, "Wis. 

301. Elizabethtown, Mt. Marcy, N.Y. 

302. Rochester, N.Y. ; Minneapolis, Minn. 



388 ELEMENTARY PHYSICAL GEOGRAPHY 



CHAPTER X. SHORE LINES 

PAGE 

308. C. S. Nos. 121, 122, 123 (New Jersey coast). 

311. C. S.Nos. 103, 104, 105 (Maine coast). 

313. C. S. Nos. 108, 109 (Massachusetts coast). 

316. C. S. No. 674 (California coast). 

322. C. S. Nos. 8100, 706 (Alaska coast). 

323. C. S. No. 21 (Texas coa.st). 



INDEX 



Adirondacks, 301. 

Africa, 55, 325, 343, 346, 350. 

Agriuulture, 43, 52, 169, 2-30, 297, 

330, 354, 364, 370, 371. 
and irrigation, 56, 71, 159, 

362. 
and soil, 150, 206, 269, 278, 

287, 296, 363. 
Air, 15, 23, 24, see Atmosphere. 
Alabama, 167. 

Ala.ska, 119, 212, 292, 299, 316. 
Allegheny mountains, 210, 273. 

plateau, 167, 243, 256, 271. 

Alluvial fans, see Fans. 
Alps, 185, 192, 203, 261, 299. 

■ glaciers of, 292, 295. 

Amazon, 41, 56, 121. 
Andes, 27, 41, 189, 190, 231. 
Anemometer, 38. 
Animals, in caves, 236. 

and climate, 335. 

• on deserts, 360. 

distribution, 332, 348. 

on islands, 330, 346. 

on mountains, 26, 169, 355. 

-in ocean, 100, 105, 122, 124, 

338. 
Antarctic ocean, 96, 104, 116. 

regions, 96, 129, 291. 

Anticyclones, 46, 75, 77, 78, 80. 
Aphelion, 12. 



Appalachian mountains, 239, 369. 
Arctic ocean, 96, 116, 130. 

regions, 103, 336, 342. 

Argentina, 139, 190. 

Arid regions, 180, 280, see Deserts. 

Aristotle, 2. 

Arizona, climate, 71, 74. 

plateaus, 165, 172. 

volcanoes, 226, 230. 

Artesian wells, 238. 

Asia, 129, 343, -345, 346. 

Atlantic ocean, 80, 84, 96, 100, 

104, 115, 130, 226, 367. 
Atmosphere, 23. 

circulation, 35, 40, 59, 304. 

color, 27, 76, 225. 

composition, 24. 

convection, 36, 60, 63. 

currents, 36, 62, 67. 

density, 26, 27. 

■ elasticity, 26. 

height, 15, 23. 

humidity, 60. 

pressure, 24, 90. 

properties, 15, 23, 29. 

saturation, 61, 63, 64. 

• weight, 26. 

Atolls, 328. see Reefs. 
Augusta, 158. 
Aurora, 18. 
Australasia, 131, 346. 



389 



390 



ELEMENTARY PHYSICAL GEOGRAPHY 



Australia, 50, 56, 71, 130, 343, 346. 
Avalanches, 192. 
Azores, 348. 

Bad lands, 283. 

Baltimore, 156. 

Banks, 109. 

Barometer, 25. 

Barriers, 167, 170, 189, 256, 333. 

Baselevel, 145, 255. 

Basin, interior, 283, 288. 

river, 241. 

rock, 296, 300, see Lakes. 

waste-filled, 284, see Waste. 

Basques, 357. 

Bays, 119, 121, 156, 211, 314. 

Beach, 112, 307, 308, 313, 320. 

Beavers, 341. 

Bench, 200, 312, 327. 

Bengal, Bay of, 69, 72, 268. 

Bering Strait, 130. 

Birds, 52, 334, 339, 341, 354. 

Black mountains, 301. 

Blizzard, 78, 81. 

Blue Ridge, 205. 

Bluff, 308, see Cliff. 

Boers, 369. 

Bolivia, 290. 

Bore, 121. 

Boundaries, 11, 190, 368. 

BoAvlders, 298. 

Brahmaputra, 268. 

Brazil, 41, 68, 325, 366. 

Brickfielders, 81. 

Bristol channel, 121. 

British Columbia, 84, 212. 

British Isles, 107, 119, 370. 

Buenos Aires, 307. 

Buffaloes, 160. 



Buran, 81. 
Butte, 171. 

Cairo, 263, 363. 

Caldera, 221. 

California, climate, 55, 71, 73. 

coast, 143, 314. 

■ fans, 267. 

moraines, 295. 

mountains, 178, 181. 

valley, 265, 266. 

volcanoes, 219. 

Calms, 43, 44, 54, 56, 57. 

Camden, 158. 

Camel, 248, 360. 

Canada, 85, 133, 255, 292, 295, 

300, 302. 
Canals, 232, 248, 320. 
Canoes, 248, 322, 352. 
Canyons, 162, 164, 166, 282. 
Cape Cod, 138. 
Cape Horn, 81, 118, 191. 
Cape of Good Hope, 81, 118. 
Carbon, 24. 
Carbonic dioxide, 24. 
Cardinal points, 7. 
Caribbean sea, 106. 
Caribou, 342. 
Cascade mountains, 73. 
Cassowary, 347. 
Catskill mountains, 167. 
Caucasus, 185, 292. 
Caverns, 235. 

Central America, 106, 226, 231. 
Ceylon, 83. 
Charleston, 158, 238. 
Chesapeake bay, 156, 238, 368. 
Chicago, 369. 
Chile, 56, 190, 280. 



INDEX 



391 



China, 189, 269, 287, 345. 

Chinese, 345, 346. 

Chinook wind, 189. 

Cinder cone, 219. 

Circles, 9. 

Cirrus, 63. 

Cities, 156, 157, 158, 209, 253, 270, 

297, 302, 368. 
Civilization, 4, 84, 139, 170, 332, 

345, 355, 364, 370, 371. 
Clay, 139, 152, 366. 
Cleopatra's Needle, 135. 
Cliff dwellers, 167. 
Cliffs, 163, 166, 167, 171, 173, 174. 

sea, 305, 310, 314, 316, 318. 

Climate, 56, 59, 82, 102, 135. 

and animals, 348, 354. 

and land forms, 278, 283. 

and man, 84, 349. 

and plants, 83, 348, 353. 

and shore lines, 323. 

changes of, 288, 318, 338. 

dry, 135, 159, 180, 281, 359, 

362. 

glacial, 290. 

of lands, 83, 133, 284. 

of mountains, 71, 183, 188, 

189, 353. 
— of oceans, 52, 83, 84, 102. 

of plains, 71, 188, 189. 

of plateaus, 165. 

Cloudbursts, 66, 166, 234, 282. 
Clouds, 37, 39, 44, 62. 
Coal, 139, 170, 366. 
Coastal plains, 143, 147, 158. 

ancient, 161. 

Atlantic, 148, 155, 158, 170. 

belted, 150. 

embayed, 154. 



Coasts, 107, 141, 211, 288, 304, 305, 

308, 316, 325, -368. 
Cold wave, 78, 81. 
Colorado, 188, 226, 282, 294. 
Colorado canyon and river, 165, 

166, 337. 
Columbia, 157, 158. 
Columbia river, 198, 229. 
Commerce, 5, 97, 349, 364, 370. 
Compass, 18. 

Condensation of vapor, 16, 39, 62. 
Conduction, 28, 31, 61. 
Cones, 219, 220, see Volcanoes. 
Connecticut, 208, 368. 
Connecticut river, 209. 
Conseguina, 223. 

Continental divide, 198, 232, 243. 
Continental shelf, 107, 133. 
Continents, 58, 129, 132, 341, 345. 
Contours, 222. 
Convection, 36, 60. 
Coral reefs, see Keefs. 
Corn, 76, 343, 348. 
Corona, 64. 
Cotopaxi, 223. 
Cotton, 148, 149, 348. 
Crater, 218, 221. 
Cuba, 106, 318, 325, 328, 366. 
Cuesta, 153. 

Cumberland plateau, 167. 
Cumulus, 63. 
Currents, 114, 116, 118, 119, 120, 

122, 306, 308. 
Cj'clones, 46, 63, 67, 75, 80, 81. 

Day and night, 7, 13, 28, 48. 
Dead sea, 284, 285. 
Deception island, 221. 
Deerfield river, 209. 



392 



ELEMENTARY PHYSICAL GEOGRAPHY 



Degrees, 9, 10. 
Delaware, 368. 
Delaware bay and river, 152, 155, 

269, 273, 368. 
Deltas, 138, 212, 267, 269, 321, 322. 

in lakes, 250, 267, 289. 

Denudation, 137, see Erosion. 

Denver, 282. 

Deposition of waste, 108, 137, 265, 

267, 283, 287. 
Deserts, 30, 41, 71, 133, 278, 280, 

286, 288, 359. 
Dew, 61, 62. 

Dikes, 132, 266, 308, 322. 
Distributaries, 268, 322. 
Distribution of life, 332. 
Divides, 190, 198, 242, 243. 
Doldrums, 43, 44, 56, 60, 65, 67, 68. 
Drainage, 168, 180, 2-34, 243, 248, 

270,-284. 
Drift, glacial, 296, 300, 302. 

• of ocean, 116, 117. 

Drought, 76, 236, 244, 359. 
Drumlins, 299. 
Dunes, 136, 287, 308, 309. 
Dust, 286, 287. 
Dwarfs, 350. 

Earth, 1, 332. 

age, 17. 

area, 129. 

astronomic relations, 11, 12, 

14, 46. 

attraction, 5, 17, 24. 

axis, 6, 354. 

crust, 16, 132, 137, 177. 

interior, 15, 16. 

proofs of shape, 2, 3, 19. 

revolution, 11, 46, 48, 49, 87. 



Earth, rotation, 6, 7, 19, 36, 57, 85. 

shape and size, 1, 3, 4, 6. 

structure, 15. 

Earthquakes,175, 180, 182, 201, 217, 

218, 224. 
Earthquake waves, 113, 114. 
Eclipse, 2. 
Ecuador, 223. 
Eddies, 115, 117. 
Egypt, 135, 363. 
Electricity, 19, 65, 253. 
Enchanted mesa, 172. 
England, 1.39, 162, 242, 314. 
Equator, 9, 29, 36, 102. 

heat, 35, 40, 49, 67, 83. 

sky, 89. 

Equatorial calms, 43, 57. 

rains, 54, 56, 72, 74, 83. 

Equinox, 88. 

Erosion, 137, 185, 245, 308, 311. 

glacial, 294, 299, 320. 

Eruptions, 219, 223, 225, 227, 231. 

Escarpment, 173. 

Eskimos, 103, 292, 324, 352. 

Estuaries, 121. 

Eurasia, 50, 129, 345, 356. 

Europe, 55, 72, 81, 84, 104, 129, 

345, 346. 
Exercises, 4, 8, 10, 12, 35, 42, 45, 

50, 51, 53, 61, 75, 83, 85, 87, 90, 

115, 259, 260, 261, 264. 

Fall line, 157, 158. 

Falls, 157, 247, 248, 251, 299, 302. 

Famines, 266. 

Fans, 179, 197, 265, 267, 268, 283. 

Faults, 174. 

Fertilizers, 150, 152, 330. 

Fiji islands, 68, 99. 



INDEX 



393 



Fingal's cave, 312. 

Fiords, 212, 320, 322. 

Fire, 24. 

Fish, 16, 100, 335, 336, 339. 

Fisheries, 109, 124, 156, 212, 320. 

Floe ice, 102, 117. 

Flood plains, 258, 261, 264, 268, 270, 

363. 
Floods, 194, 244, 250, 256, 264, 266, 

281, 282. 

and lakes, 194, 250. 

sea, 69, 308. 

Foehn wind. 189. 

Fog, 64. 

Forests, 149, 159, 168, 170, 348. 

effects of, 236, 310, 350. 

on mountains, 41, 43, 187, 189. 

192. 204, 205, 355. 
Fort Wayne, 320. 
Fossils, 108, 133, 161, 183, 185, 338, 

337. 
France, 310, 311, 313. 
Frigid zone, 29, 75, 80. 
Frost, 61, 62, 135. 
Fundy, Bay of, 121. 

Galapagos, 119, 325, 348. 

Gales, 38, 80. 

Galung-gung, 223. 

Galveston, 69, 238. 

Ganges, 195, 268. 

Gases, 15, 23, 24, 100, 216, 218. 

Geology, 158. 

Geosphere, 17. 

Germany, 272, 295. 

Geysers, 239. 

Gibraltar, 106, 315. 

Glacial period, 295, 319. 

Glacier, 104, 188, 278, 292, 294, 322. 



Glacier, Alpine, 187, 250, 292, 295. 

ancient, 294, 299. 

continental, 290, 295. 

. — Laurentian, 295. 

Scandinavian, 296. 

valley, 292, 294. 

Glens, 205. 

Globigerina, 105. 

Gloucester, 109. 

Gold, 139, 191. 

Gorges, 184, 201, 251, 301. 

Grand canyon, 165. 

Grand Kapids, 302. 

Granite, 234. 

Gravity, 5, 24, 358. 

Grazing, 56, 71, 74, 160, 181, 294, 

354, 359. 
Great Barrier reef, 327. 
Great Britain. 370. 
Great lakes, 248. 284, 295, 319. 
Great plain.s, 71, 73, 158, 366. 
Greek philosophers, 3, 19. 
Greely, 103. 

Greenland, 104, 291, 321, 335, 351. 
Greenvyich, meridian of, 10. 
Ground water, 234, 236, 239, 283, 

362. 
Guam, 99. 

Guiana, 118, 158, 173. 
Gulf Stream, 116, 118 

Hail, 70. 
Halo, 63. 
Harbors, 40, 119, 120, 143, 147, 152, 

212, 307, 311, 320, 368. 
Harrisburg, 274. 
Hawaiian islands, 106, 325. 
Headlands, 311, 314. 317. 
Heat, 24, 28, 30, 46. 



394 



ELEMENTARY PHYSICAL GEOGRAPHY 



Height of land, 241, 319. 

Hell Gate, 122. 

Hemispheres, 9, 46, 52, 53, 54, 96. 

Herculaneum, 224. 

Highlands of Scotland, 205, 318. - 

Himalayas, 71, 185, 189, 193, 200, 

202, 294. 
History and nature, 170, 205, 321, 

357, 361, 367. 
Hoang-Ho, 265, 268. 
Horizon, 19. 

Horse latitudes, 44, 45, 55. 
Hot springs, 239. 
Hudson bay, 50. 
Hudson river, 368. 
Humboldt current, 118. 
Humidity, 60. 
Hungary, 262. 
Hurricane ledge, 173, 175. 
Hurricanes, 67, 69, 112. 

Ibex, 356. 

Ice, 15, 63, 102, 117, 279, 291, 323. 

falls, 192. 

sheets, 290, 291, 294, 319. 

See Glaciers. 
Icebergs, 104, 291, 292. 
Iceland, 226, 227, 239. 
Idaho, 229. 
Illinois, 320. 
India, 72, 189, 194, 269. 
Indiana, 320. 
Indian ocean, 58, 68, 69, 96, 115, 

226. 
Indians, 172, 321, 361. 
Inlets, 152, 308. 
Instinct, 341. 
Intelligence, 341. 
Iowa, 238. 



Ireland, 116. 
Iron ore, 139, 170, 366. 
Irrigation, 56, 71, 159, 265, 362. 
Islands, 50, 131, 314, 320, 346, 370. 

continental, 211, 212, 311. 

coral, 106, 325, 328, 330. 

oceanic, 106, 131. 

volcanic, 106, 219, 225, 226, 

348. 
Isobars, 91. 

Isothermal lines, 33, 35, 48, 50, 53. 
Italy, 225, 269, 314. 

Jaguar, 343. 

Japan, 114, 203, 225, 345. 

Java, 223. 

Jetties, 322. 

Jorullo, 219. 

Jura, 183, 184. 

Kanawha river, 169. 
Kangaroo, 344. 
Katahdin, Mt., 357. 
Kentucky, 170, 235. 
Kittatinny Mountain, 273. 
Krakatoa, 27, 113, 225. 

Labrador, 51, 119, 370. 

Lagoons, 308, 328. 

Lake Bonneville, 288, 319. 

Crater, 222. 

-Erie, 248, 251, 320. 

Geneva, 250, 207. 

Great Salt, 284, 288, 290. 

Lahontan, 289. 

Lob, 285. 

Michigan, 320. 

Nicaragua, 231. 

Nyassa, 249. 



INDEX 



395 



Lake Ontario, 248, 251. 
— - Superior, 248, 366. 

Titicaca, 290. 

Van, 284. 

Victoria Nyanza, 249. 

Lakes, 160, 230, 235, 247, 240, 263, 
284, ^89, 319. 

African, 249. 

glacial, 296, 300. 

in mountains, 197. 

-salt, 181, 283. 

sliore lines, 133, 288, 318. 

temperature, 102. 

volcanic, 222, 228, 249. 

Land and sea breezes, 59. 
Land hemisiDhere, 96, 129, 341. 
Lands, 129. 
— - altitude, 4, 131, 132. 

area, 129. 

distribution, 130. 

features, 133, 141, 177, 256. 

life on, 338. 

products, 138. 

surface, 26, 133, 134, 136. 

winds on, 59. 

Land sculpture, 186, see Waste. 
Landslides, 138, 193, 202. 
Language, 4, 205, 226, 357. 
Latitude, 8, 10, 54, 89, 342. 
Laurentian highlands, 247, 295. 
Lava, 15, 16, 216, 225, 330. 
— - flows, 219, 227, 230, 249. 
— - plateaus, 227, 228, 229. 
Lawrence, 302. 
Ledges, 135, 247, 286, 306. 
Levees, 264. 
Life, 17, 24, 122, 332. 
Light, 24, 27, 64, 66, 124. 
Limestone, 139, 235. 



Llanos, 344, 353. 
London, 96. 
Long Branch, 309. 
Long Island sound, 208. 
Longitude, 8. 
Lowell, 302. 
Luray cavern, 235. 

Magellan, 3. 
Magnetic poles, 18, 19. 
Magnetism, terrestrial, 17, 332. 
Maine, 212, 297, Sll', 357. 
Malay peninsula, 58, 366. 
Mammals, 340. 
Mammoth, 134. 
ISIammoth cave, 235. 
Man, 1, 189, 204, 345. 

and nature, 332, see Nature. 

civilized, 364, see Civilization. 

■ in deserts, 360. 

in mountains, 204, 205, 357. 

savage, 329, 349, 365, 371, 

warfare, 369. 

Manchester, 302. 

Mangrove, 324. 

Manufactures, 139, 157, 159, 209, 

252, 301, 364, 370, 371. 
Maps, 386. 

Marshes, 152, 160, 170, 308. 
Marsupials, 344. 347. 
Maryland, 211, 238, 274, 368. 
Massachusetts, 132, 208, 299. 
Meander belt, 263. 
Meanders, 261, 271, 273. 
Mediterranean, 106, 226. 
Merced river, 265. 
Meridians, 8, 9, 10, 11. 
Merrimac, 302. 
Mesa, 171, 172. 



396 



ELEMENTARY PHYSICAL GEOGRAPHY 



Meteors, 23. 

Mexico, 41, 146, 226, 280. 

Gulf of, 74, 107, 118, 322. 

Mining, 139, 170, 183, 3.33. 

Minneapolis, 302. 

Minnesota, 366. 

Mirage, 30, 286. 

Mississippi river and valley, 65, 67, 

71, 74, 76, 138, 255, 262, 264, 319. 

delta, 268, 322. 

flood plain, 264. 

meanders, 262, 263, 264. 

Missouri, 271, 278. 

river, 198. 

Mist, 64. 
Mohawk, 258. 
Monadnock, 207. 
\ Monsoons, 57, 58, 72. 
Monte Nuovo, 218. 
Months, 47, 48, 50. 
Moon, 2, 13, 124. 
V Moraines, 293, 295, 297. 
Mountains, 43, 133, 177. ■" 

air on, 26, 29. 

block, 178. 

buried, 285. 

climate of, 188. 

dissected, 181, 196, 301. 

■ effects of, 170, 180, 185, 189, 

356, 357, 369. 

embayed, 211. 

folded, 183, 210. 

growing, 201, 204. 

lofty, 27, 185, 188, 196, 204, 

355. 

old, 196, 206, 210. 

subdued, 204, 301. 

worn-down, 206. 

young, 180, 204, 205. 



Mt. Blanc, 187, 295. 
Mt. Mazama, 222, 230. 
Mud volcanoes, 241. 

Nansen, 103, 117. 

Narragansett bay, 368. 

Natural bridge, 236. 

Nature and man, 170, 204, 205, 321, 

332, .357, 361, 364, 367. 
Navigation, 10, 18, 40, 43, 58, 69, 81, 

97, 104, 116, 118, 120, 248, 370. 

river, 157, 365. 

Nebraska, 283. 
Nebular hypothesis, 14. 
Neckar river, 272. 
Netherlands, 132, 309, 310. 
Nevada, 73, 178, 181, 204, 280, 283. 
New England, 80, 109, 209, 212, 

255, 298, 31.3. 
Newfoundland, 104, 109, 119. 
New Hampshire, 207, 357. 
New Jersey, 112, 132, 152, 308, 366, 

368. 
New Mexico, 171, 172, 230. 
New Orleans, 323. 
Newton, 6. 
New York, 239, 258, 301, 360, 368. 

city, 122, 369. 

New Zealand, 90, 131. 

Niagara, 138, 248, 251. 

Nile, 56, 249, 363. 

Nimbus, 64. 

Nitrogen, 24. 

Nomads, 160. 

Noon, 7, 8, 88. 

Norfolk, 156. 

Normandy, 311, 321. 

Nortli America, 43, 72, 78, 80, 107, 

344, 346. 



INDEX 



397 



North Carolina, 74, 148, 150, 205, 

318. 
North Dakota, 298. 
Northern lights, 18. 
Northmen, 321. 
North pole, 9, 18, 36. 
North Star, 6. 
Norway, 119, 226, 299, 318, 320. 

Oases, 361. 

Occupations, 52, 157, 162, 169, 170, 

185, 209, 258, 358, 364, 365, 366, 

370, 371. 
Ocean, 90, 304. 

action, 107, 112, 121, 305. 

air, 60, 100. 

bottom, 98, 105, 123. 

color, 100. 

composition, 100. 

currents, 114, 116, 118. 

density, 100. 

depth, 96, 90, 131. 

distribution, 15. 96, 129, 130. 

explorations, 3, 98, 103. 

form, 96. 

life in? 100, 105, 122, 338. 

phosphoi'escence, 100, 124. 

storms, 80. 

temperature, 28, 98, 101, 107. 

waves, 109, 111, 113. 

Ohio, 168, 170. 

Ohio river and valley, 71, 170, 250. 

Ooze, 105. 

Oregon, 146, 178, 182, 204, 229, 

249. 
0.sage river, 271. 
Ox-bow lake, 263. 
Oxygen, 24. 
Ozark plateau, 278. 



Pacific ocean, 68, 80, 84, 96, 99, 

105, 115, 119, 226, 328. 
Pacific slope, 43, 72. 
Pamlico sound, 155. 
Pampas, 190, 344, 366. 
Panama, 315, 316. 
Parallels, 9, 10. 
Parana, 56. 
Pass, 190. 

Patagonia, 190, 292, 318, 321. 
Peaks, 178, 185, 186, 191, 356. 
Peneplain, 206, 208, 210, 246. 
Pennsylvania, 210, 271, 273, 360, 

368. 
Pei'ihelion, 12. 
Persia, 285. 
Peru, 60, 71, 359. 
Peruvian current, 118, 325. 
Philadelphia, 158. 
Philippine islands, 3, 69. 
Piedmont belt, 149, 206, 243, 271. 
Pikes peak, 356. 
Pittsburg, 170. 
Plains, 141, 158, 161, 369. 
coastal, 143, 147, 150, 154, 269, 

307, 318. 

glacial, 296. 

river-made, 266, see Flood 

plains. 
Planetary circulation, 37, 40. 
Planetary winds, 39. 
Planets, 12, 13, 14, 17, 19. 

distance and diameter, 14. 

Plants, 24, 52, 83, 235, 341, 346, 

353. 

distribution, 332, 337, 348. 

in oceans, 123, 124, 338. 

on deserts, 359, 362. 

on mountains, 355. 



398 



ELEMENTARY PHYSICAL GEOGRAPHY 



Plants on plateaus, 165. 
Plateaus, 162, 165, 171, 173. 

■ dissected, 167, 278. 

Platforms, 163, 318. 

Platte river, 261. 

Po, 295. 

Polar regions, 29, 64, 72, 75, 290. 

Poles, 9, 18, 29. 

Pompeii, 223. 

Population, 169, 170, 189, 370, 371. 

of mountains, 201, 204, 357. 

of river-made plains, 258, 260, 

269, 270, 363. 
See Settlements. 
Porto Rico, 100. 

Ports, 147, 157, 309, see Harbors. 
Potomac river, 211, 269, 368. 
Prairies, 71, 170, 296, 366. 
Prevailing westerly winds, see 

Winds. 
Prime meridian, 10. 
Problems, 9, 10, 35, 50, 90. 
Products, 138. 

Promontories, 211, 311, 313. 
Pyrenees, 190, 357. 

Race, tidal, 122. 

Races of men, 189, 204, 205, 345. 

Radiation, 28, 46, 61. 

Railroads, 97, 160, 191, 201, 371. 

Rainbow, 66. 

Rainfall, 38, 44, 65, 70, 72, 2.34. 

and trade winds, 41, 44, 55. 

and westerly winds, 43, 55, 

159. 
distribution of, 41 , 43, 56, 59, 

71, 72, 180, 183, 188, 280. 3-59. 

equatorial, 56, 72, 74, 83. 

subequatorial, 56, 353. 



Rainfall, subtropical, 55, 56, 354. 

Rain gauge, 70. 

Raleigh, 158. 

Rapids, 166, 247, 251, 255. 

Reaches, 255. 

Reefs, coral, 324, 326, 327. 

sand, 152, 156, 308, 313, 314. 

Refraction, 64, 66. 

Reindeer, 342. 

Relief, 147, 185, 210, 284. 

Rhine, 309. 

Rhode Island, 368. 

Rhone, 250. 

Richmond, 158. 

Ridges, 185, 186, 190. 

Rio Grande, 323. 

Rivers, 241, 245, 261, 265, 269, 

302. 

graded, 254. 

mature, 246, 254, 269. 

old, 246, 270. 

revived, 271. 

withering, 281, 283, 285. 

young, 246, 257, 271. 

Roads, 143, 1-56, 169, 185, 190, 

209, 247, 256, 2-58, 3^8, .320. 
Rochester, 302. 
Rock basins, 296, 300. 
Rock waste, see Waste. 
Rocks, 15, 108, 134, 1.36, 138, 235. 
Rocky mountains, 71, 74, 185, 188, 

200, 2.39, 243, 281, 294. 
Roraima, 173. 
Rotation of earth, 6, 7, 36, 57, 85. 

Sahara, 41, 42, 50, 56, 71, 83, 280, 

286, 354, ,361, 362. 
Salinas, 290. 
Salt, 290, see Lakes. 



\ 



INDEX 



399 



Sand, 286, 308, 310. 

reefs, see Reefs. 

Sandstone, 107, 209. 

San Francisco, 369. 

Saratoga Springs, 239. 

Sargassum, 123. 

Satellites, 13. 

Saturation, 60. 

Sault Ste. Marie, 248. 

Savannahs, 148. 

Scandinavia, 296, 321. 

Schuylkill, 153, 158. 

Scotland, 145, 205, 317, 318. 

Seas, 106. 

Seasons, 46, 49, 50, 56, 76, 77, 78, 

83, 353. 
Seaweed, 123. 

Sediment, 101, 100, 108, 121, 148. 
Seine, 121. 

Selkirk mountains, 188. 
Settlements on coasts, 143, 156, 

212, 314, 318, 320, 368. 

deserts, 285, 361, 363. 

• ^ mountains, 181, 183, 185, 216. 

plains, 146, 159, 206, 297. 

plateaus, 165, 166, 171, 278. 

rivers, 209, 252, 258, 302, 363. 

See Population. 
Shasta, Mt., 222, 229, 231. 
Sheavwits plateau, 173, 174. 
Ships, 4, 40, 69, 98, 103, 120, 212. 
Shir6 river, 249. 
Shore lines, 132, 155, 304, 307, 311, 

317, 323. 

of deltas, 322. 

of lakes, 133, 288, 318. 

Siberia, 81, 134, 160. 
Sierra Nevada, 73, 189, 295. 
Silt, 255, 263, 265, 269. 



Sink holes, 235. 

Sirocco, 81. 

Sky, 19, 27, 62, 76, 78, 89. 

Snake river, 229, 288. 

Snow, 70, 77, 187, 190, 192, 290. 

line, 29, 355. 

Soil, 23, 135, 148, 152, 158, 296, 

362. 
Solar system, 14, 17. 
Solstice, 88. 
Sound, 27, 66, 340. 
Sounding, 98. 
Sounds, 212. 

South America, 343, 344, 346, 366. 
South Carolina, 148, 157. 
Spain, 139. 

Springs, 236, 239, 361. 
St. Bernard pass, 190. 
St. Gotthard, 193. 
St. Helena, 112. 
St. Lawrence, 80, 247, 248, 250, 

284, 319. 
Stacks, 312, 317. 
Stars, 12, 19. 
Steppes, 354. 

Storms, 64, 65, 66, 67, 79, 80. 
Streams, 235, 236, 241, 281. 
Subequatorial belts, 55, 56, 71, 83, 

353. 
Subtropical belts, 55, 56, 73. 
Sudan, 83. 
Sulu sea, 107. 

Sun, 7, 11, 14, 46, 48, 87, 125. 
Sunrise and sunset, 7, 27, 89, 225. 
Surf, 40, 58, 111, 304, 313. 
Susquehanna, 269, 271, 274, 368, 
Svanetian.s, 357. 
Swamps, 150, 296, 313, 324. 
Sweden, 132. 



400 



ELEMENTARY PHYSICAL GEOGRAPHY 



Swell, 111. 

Switzerland, 189, 199, see Alps. 



Turks, 346. 
Typhoons, 67, 69. 



Table mountains, 171. 

Talus, 163, 166, 178, 180. 

Tarim river, 285. 

Temperate zone, 59, 75, 78, 80, 84. 

Temperature of atmosphere, 28, 

32, 34, 37, 46, 49, 61. 

and currents, 118. 

charts, 33. 

mean annual, 33, 34, 50. 

of earth, 16, 134. 

of lakes, 102. 

of oceans, 28, 98, 101, 118. 

Terraces, 200. 
Texas, 74, 323. 
Thermograph, 32. 
Thermometer, 31, 32. 
Thunderstorms, 44, 65. 
Tiber, 138. 
Tibet, 26, 226. 
Tides, 119, 122, 126, 268, 304. 

cause of, 120, 124. 

Time, 7, 11, 46, 49. 

Tin, 366. 

Tonga Islands, 219. 

Tornadoes, QQ. 

Torrents, 197, 253, 254, 280. 

Torrid zone, 29. 48, 59, 60, 74, 

80. 
Trade winds, 39, 40, 55, 57, 71. 
Transportation of waste, 137, 164, 

168, 188, 196, 246, 270. 
Tree line, 355. 
Trenton, 158. 
Tributaries, 168, 254. 
Tunnels, 191, 193. 
Turkestan, 285. 



XJinkaret plateau, 173. 

United States, 158, 170, 191, 338, 

371. 

boundaries, 11, 368. 

■ coasts, 148, 158, 368. 

development, 371. 

glacial action in, 295, 296, 

302. 

products, 76, 139, 348, 371. 

rainfall, 72. 

weather, 75, 76, 77, 82, 291. 

winds, 42, 63, 79, 81. 

See Rivers, Lakes, Plains, etc. 
Utah, 71, 73, 181, 280, 283, 319. 

Valleys, 136, 209, 256, 259, 270. 

crosswise, 200. 

drowned, 154, 156,269, .368. 

filled, 199. 

hanging, 299, 300, 322. 

■ in mountains, 185, 196, 358. 

in plains, 143, 145, 154, 159. 

in plateaus, 162. 

lengthwise, 200. 

terraced, 200. 

Vapor, 38, 41, 60, 62. 

Variation of plants and animals, 

337, 338. 
Vegetation, 43, 159, 181, 187, 235, 

350, 353, 355, 359. 
Venezuela, 56, 353. 
Vera Cruz, 147. 
Vermont, 208. 
Vesuvius, 221, 223. 
Vikings, 321. 
Vineyard sound, 67. 



INDEX 



401 



Virginia, 156, 206, 210, 318, 368. 
Volcanoes, 16, 106, 113, 133, 215, 
216, 220, 223, 226, 229, 231. 

Wadies, 281. 

Wales, 205, 

Washington, 72, 229, 366. 

Waste of the land, 134, 136, 163, 

245, 254. 

and climate, 135, 323. 

deposition of, 108, 137, 265, 

267, 283, 287. 

glacial, 279, 293, 296. 

in basins, 284, 209. 

in valleys, 183, 197, 199, 284. 

on shores, 107, 112, 141, 304. 

transportation of, 137, 164, 

168, 188, 196, 246, 270. 
Water, 15, 38, 96, 102, 136, 234. 

circulation of, 39. 

hemisphere, 96, 129. 

power, 252, 301, 302. 

Waterfalls, see Falls. 

Water gaps, 210, 273. 

Watershed, see Divide. 

Waterspouts, (H^. 

Water vapor, see Vapor, Rainfall. 

Waves, 109, 111, 304, 306, 308, 

311, 316. 

earthquake, 113. 

Weather, 42, 59, 74, 76, 77, 78. 

bureau, 82, 90. 

maps, 33, 81, 90. 

prediction, 81. 

Weathering, 1.34, 163, 183, 186, 

200, 205. 206, 209, 312. 
Wells, 237, 238. 



We.st Indies, 69, 106, 133, 325. 

West Virginia, 167, 170, 236, 278. 

Wheat, 77, 348. 

Whirlwinds, 66. 286. 

White mountains, 357. 

White Sulphur Springs, 239. 

Winds, 36, 37, 39, 79, 85, 91, 189. 

and currents, 115. 

and denudation, 136, 286. 

anticyclonic, 46, 75, 78, 80. 

cyclonic, 46, 63, 67, 75, 78, 

80, 81. 

daytime, 60. 

land and sea breezes, 59. 

of continents, 58. 

planetary, 37, 39. 

prevailing westerly, 39, 42, 

44, 51, 54, 63, 72, 75, 80, 334. 

terrestrial, 53, 76, 77, 79. 

trade, 39, 40, 44, 55, 57, 71. 

velocity, 38. 

westerly, see prevailing wes- 
terly. 

whirls, 39, 40, 42, 44. 

Windward islands, 40. 

Wisconsin, 161, 238. 

World, Old and New, 130, 343, 
367, 371. 

Yakima river, 257. 
Yellow .sea, 101, 268. 
Yellowstone park, 198, 239, 240. 
Yellowstone river, 251. 
Yucca, 360. 

Zenith, 89. 

Zones, 29, 46, 48, 52, 348. 



PLATE A. 




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